Ok, how about something like this: Manchuria is conquered on schedule, but due to <insert PoD here> it is even more costly in blood and treasure than in OTL, somewhat discrediting both the current army leadership and foreign adventurism in the eyes of the public. Japan never joins the Anti-Comintern Pact. The armies in Manchuria, bowing to public opinion and (somewhat) to the leadership in Tokyo, draw down to garrison strength, preventing a wider war in China or Soviet border skirmishes. The Navy largely escapes the negative feelings associated with the Army, but the prevailing mood is still enough to make the level of naval expansion seen in OTL politically impossible.
The war in Europe goes on as OTL, and eventualy the secret war in the North Atlantic draws the US into the fray. US-Japanese tensions remain low, however, so there is no trade embargo and no fleet at Pearl. Eventually, strong lobbying and don't-miss-the-bus-ism (TM) combine to convince the powers that be to seize the Southern Resoure Area while the Western Colonial Powers are distracted by the war in Europe. At least at first, the Japanese leave American possesions alone. The US is forced to declare war on Japan, as all its allies in the European War are also at war with Japan. However, the US public largely views this part of the conflict as a squabble over imperial holdings, and the moral outrage seen OTL does not exist.
Japan quickly conquers the areas it targets, but soon after the US begins slowly but surely destroying the IJN. Soon Japan can no longer resupply its forces in the field, but the Allies are not eager to root out the IJA island by island. The stage is set for a negiotated peace. As an aggressor nation, Japan must be punished, but already some are calling for liency. Allied capitols are filled with worried talk about the strength the USSR is set to have in the post-war world, and Japan could be a vauble ally...
In the end, Japan returns all newly captured territory, plus most of the mandate islands go to the US. Manchuria and the Kwantung Leased Territory go to China, but Japan retains Taiwan, Karafuto, and Chosen.
Comments/critiques?