With rgard to African 'tribes' fighting taking up arms against each other because of a European war, that's pretty much ASBs.
Maybe get the Wadai (one of the last African states conquered before WWI) to fight Darfur, who were also not fully conquered at the time (they were conquered during WWI)? You'd have to delay the Wadai War a few years to set that up, but you might be able to get an Allied Darfur (as a nominal tribute of Britain) and a CP Wadai. But looking at Darfur's internal politics, they'd need to convince the Sultan that Britain was the winning side and allying with the Turks/Germany is a foolish choice.
Other than that, more indigenous revolts in Africa during the Great War, preferably led by the traditional monarchs of the region who both still existed and still had significant authority amongst the people. You can even have some of them fight each other, since a lot of the aforementioned traditional monarchs and states that were conquered in the Scramble for Africa utterly hated each other (at least in West Africa). France could use it to drive a wedge in any potential anti-colonial alliance, although at the cost of territory and signficant face. Of course, Germany might not be in any position to be inspiring revolts in Africa, looking at their own colonial situation in Africa.