@Gargantua:
Unless you are at war with Japan it cannot be done.
Because being at war on one board, vs being at war on another board have no relation to each other.
Yes. However, there is no restriction for the US or Russian players to keep all their starting units on a particular board until they are at war on both boards. The US player is free to move Pacific units into the European theatre and vice-versa, however, they wouldn’t be able to do that without violating the European movement rules, which is why I said they would have to wait in India until they are at war in Europe. Unlike the Russians, once attacked by Japan they can declare war on the Euro-axis, so as soon as they at at war with Japan they can DoW Germany or Italy and open up the NCM into Persia, which they will then be able to reach from India.
I’m not sure why you say this scenario is implausible. Impractical might be a better word.