In talking about getting the Japanese to win in the Pacific, the overriding concern is that Japan is fundamentally not self-sufficient in production. Oil (1939 - 80% from US) is of course the obvious one, but steel (1938 - 75% US scrap), chemicals, machine tools, and minor minerals (vanadium, copper etc) were critical too. And this is just talking about dependence on US - we've not even gotten into whether Japan actually has the forex to pay for such imports. In 1936 alone, half of Japan's gold reserves were sent overseas to pay for imports, and boosting exports (cotton, specie) would require diverting resources from the military. Japanese leaders knew this and knew that (despite arguments, threats, and changes to the Planning Board) this meant that a long-term, attritional war against the rearming US (2nd Vinson Act, 1938) was not winnable.
The idea, in 1941 at least, was to bring on such a heavy strike in the Far East, coupled up with German success, that the US would be distracted and thus buy Japan some breathing room to set up a self-sufficient industrial system or pose itself as a bulwark against Soviet Communism. This strategy, as OTL showed, was doomed to failure, not least because Japan's industrial situation at that time was so poor (with prior US embargoes and lack of forex already causing major drops in production everywhere) that it was not possible for the country to replace losses not just in military units, but even in its shipping and logistics network which underwrote the whole structure of Japanese imperialism.
So changes have to start with the 1937 escalation in China, which began the cycle of increased Japanese spending, increased reliance on imports and American embargoes that ultimately led to Pearl Harbor. OTL, Tokyo in 1937 was interested in a stable regional environment in order to build up its industrial base in Manchukuo as a prelude to war with the Soviets in the mid-1940s, but when push came to shove it was neither able to stop the Kwantung Army nor was it willing to sacrifice its 'informal empire' in North China (at least not until it was too late). Ultimately, Tokyo would have to make the concessions instead of forcing China, because Chiang was being pressured by public opinion to take a strong stand against Japan.
Even more difficult, Tokyo would have to resist the urge to militarily move against the Soviet Union or the orphaned European colonies once WWII starts, both actions that would be taken very badly in the US as it would likely be seen as indirect aid to Germany. One could make a case for Tokyo sidling up to Germany since Germany (through the Soviets) was a key exporter of materials to Japan.
That isn't to say that Tokyo can't make life difficult for the Allies, however. An overtly-peaceful Japan with a stronger industrial base will be able to make 'reasonable demands' of French Indochina, Malaya and the DEI that would be hard(er) to resist. OTL, this was what Japan hoped to achieve; but in both cases their demands were essentially waved off as the China War made Japan's hostile intentions clear. A hostile posture towards the Soviet Union might also prevent the transfer of units to Germany. All the while, Japan continues to develop its industry and lessen/diversify dependence on imports, if not on oil then at least in other raw materials and industrial goods.
Even if this strategy doesn't save Germany, it places Japan in a very strong position to dominate the postwar space in China and SE Asia. Being militarist alone is not a reason for the US to crusade against Japan, as Franco's survival showed; indeed, it's not even clear that the anti-colonial US would actually take all that much offense to Japan sponsoring its own independence movements against the British, French and Dutch postwar. The strength of Japan's economy and its 'success story' allure to the peoples of Asia (this includes China) would almost ensure the establishment of an 'informal/commercial empire' across the region, with Japan now becoming a mini-US in the supply of industrial goods to Asia.
I realize this is not a Pacific War, but in terms of achieving what Japan intended to achieve through its doomed Pacific War (self-sufficiency and space for itself in Asia), this pretty much covers it.