Well, one can always try and see what will happen. One learns this game best by trying crazy things...
I think that in one of my solitair games, I probably will DoW Japan with the CW, France and the USSR early 1940, to kill as many Japanese convoys as possible during the surprise impulse. A side effect is that there is no more oil going from NEI to Japan. Sure, this means that the US can't DoW Japan anymore, but if option 50 has been chosen later in the game, the US carriers can still attack the Japanese ships at will and they can carry CW units into invasion positions...
I remember reading in a WiF annual about some game at a WiFcon where everyone declared war on Japan early. The rules were different back then, with incredible restrictions on what Japan could do so long as the convoy chain was broken, and Japan got conquered fast. I think they changed that rule very soon thereafter.
I thought I knew how to play this game....