It's not really that hard, after all the USSR and Germany were quasi-allies in 1940.
All you need is:
All you need is:
- Hitler must die, and if possible be replaced by Goering, who apparently didn't quite like the idea of attacking the USSR, or some military clique that realizes that their strategic situation would only worsen if they did go to war with Stalin.
- The Allies bomb Baku to stop oil shipments to Germany, send troops to Finland bia Norway and Sweden or both; these were plans the Allies considered in 1940 after all.
- Then, all you need is Japan attacking the European colonies looking for a quick grab; if the Allies and/or China push too much north the Soviets may end up sending troops to help the Japanese in Manchuria.