How about the POD that Menelik II lives three healthy years longer:
Ras Tafari becomes the governor or Harar in 1910, as OTL, and skilfully administrates the region, instituting some successful reforms. However, due to Menelik II being longer-lived, subsequent rumours of talks between the British and the Ethiopians, and Ethiopia being somewhat more threatening to the Germans leads them to attempt to raise the Harar people to revolt for religious reasons. This attempt is led secretly by Leo Frobenius, a personal friend of the Kaiser (this is OTL), but he is stopped and arrested by Tafari. Menelik II, after negotiations with the Germans break down and Menelik actually gets British support orders Frobenius executed for enticing revolt (Ethiopia is tense around it's Muslim minorities). The Kaiser is extremely angered by this, as he is a personal friend of Frobenius, and orders Ethiopia to be treated as if it was hostile. Menelik officially declares war over this, and, in exchange for British promises of diplomatic support against Italy's desire for more of Ethiopia, decides to send an expeditionary force of a few thousand men, equipped by the British.
With Ras Tafari being essentially the face of Ethiopia to the British, having been their main negotiating partner and having a good relationship with them, Tafari heads off to help guard the Suez with this force. Agitating for actual combat, Tafari convinces the British to let him take his forces to fight, and turns his knowledge of court politics to raising Ethiopia's image abroad, inviting journalists to his headquarters, speaking to them in English and generally being a propaganda device. Somewhere in here Menelik decides to name him as the heir. The Ethiopians gain a reputation for aggressiveness, hand-to-hand fighting and hard, fast marches against the Ottomans, and have a love affair with every black reporter talking about the war.
With Menelik's health failing by mid-1916, Tafari convinces the British to allow him to take his now British-equipped small army back to Ethiopia to secure his succession, with a new cohort of Ethiopians arriving to replace them. The British see 3000 Lee-Enfields, a few artillery guns and some shipping tonnage a fair price for a friendly Ethiopia. Tafari successfully crushes competition from Ethiopian feudal lords, because he has things like artillery guns, thanks to the British.
On his way home from his travels, the Afro-Caribbean missionary Marcus Garvey met in OTL (who had spent time in Basutoland and taken a Basuto wife, but traveled via the Suez here where he met Tafari and his expeditionary force) he met tells him of Tafari and Menelik, which reinforces his admiration of the last free African state. Garvey's UNIA is a bit more successful and embraces Ethiopianism a bit more, so, in 1917 he decides to travel to both Ethiopia. Garvey is also more tolerated by the British due to his support of Tafari and the Ethiopians fighting in the Middle East.
Ras Tafari is crowned in 1916 as Haile Selassie, at the age of 21, not having to act as regent as in OTL. He invites journalists and foreign dignitaries to Ethiopia, sends gifts to various world leaders and helps put Ethiopia and his expeditionary force into the papers in the west. He also starts speaking out against colonialism, worried of becoming a British protectorate with the end of the war, so he echoes Wilson's self-determination sentiments.
Rastafarianism appears early, seeing Selassie as the savoir of the African race. Rastafari expands in Jamaica, bolstered by the greater prominence of Haile Selassie being a great reformer and conscious of the utility of public opinion (Newspaper images of the old darling of the media from the war freeing the last slaves in Ethiopia will really be excellent for the Rastas popularity).
Selassie manages to put through a marriage between one of his relatives and a relative of the Emperor of Japan, as was discussed in OTL. Ethiopian coffee becomes a status good in certain circles in Japan.
Fast forward to the second Italio-Ethiopian war, and Mussolini's forces do even worse, with Ethiopia possessing a far more modern military, and Selassie makes the Italian use of gas into an even greater issue by putting journalists right in front of it. Marcus Garvey spearheads a movement to find volunteers and resources to send to Ethiopia in it's struggle, but manages to involve even white, upper-class anti-imperialists, as well as the Afro-Carribian movement. Ethiopia is not fully subjugated by the time WW2 starts, with large guerilla forces under Selassie's command-in-exile, extracting serious tolls on Italy. For this reason, Italy doesn't run it's own invasion of France until the French are almost fully defeated, and the Japanese Imperial Family actually criticizes the Italians for attacking what they see as their friend. Tensions in the tripartite pact rise.
The forces still fighting in Ethiopia up until WWII's start include Rastas and other African Liberationists, who are armed and trained by the allies. Haile Selassie starts to be viewed as a savoir, even by the Ethiopian soldiers, due to both their interaction with Rasta volunteers, and his constant fight, although they don't see him as the second coming of Jesus. By the end of WWII, the Rasta fighters are brought back to Jamaica by Garvey's Black Star Line, which also smuggles their arms back to the country, although no violence occurs yet. As India moves towards independence, several ANC leaders mention Jamaica in the context of international struggle against colonialism.
Fearful of the numbers of armed Rastas agitating in the country, Jamaican independence comes in 1955, with the Rasta community being a part of the new government. Marijuana is quietly legalized for religious purposes on the island. The WWII Rasta fighters or their children join Jamaica's new military, making it almost 70% Rasta. The religion keeps growing, and at the height of the Civil Rights movement in the US, it crosses into the US. The Black Star Line is now the national shipping company of Jamaica. In the 1967 election, a privately Rasta president is elected to be the PM of Jamaica, and runs a pair of referendums to remove the Queen as the Head of State and replace her with Haile Selassie. The first referendum succeeds, but the second fails, so the Rasta PM becoming the President of Jamaica. A military coup plot against the President is foiled when Rasta soldiers learn of it, and the offending Generals are imprisoned, boosting the President's popularity by making the opposition appear anti-democratic.