After the collapse of France in June 1940 the US Army & Navy Chiefs of Staff begain a study of how to fight the Germans. This took the form of a series of estimates that eventually evolved into what became known as the 'V Plans' . One of these estimates assumed the USSR would be defeated and driven out of Europe. In this case it was projected the US would need to produce enough equipment/supplys to mobilize and sustain over 200 infantry and armor divsions and the equivalent in airforces. Plus extra cargo ships. Not all the manpower for these were to come from the US. It was assumed that as with the Poles a large remanant of the Soviet army would escape and provide a pool of manpower to be rearmed. The general idea was the US and sponsored forces would build up around the periphery of the nazi conquests until airpower wrecked the German industry and transportation leaving the nazi armys inadaquately supplied.

Plans were started for establishing a suitable logistics base in the Persian Gulf region. The establishment of the Lend Lease supply route through Persia was a step towards this. The Siberian route (through which most Lend Lease actually moved) was also considered. The ability of Japan to interfere with this made it risky. The northern route to Murmansk was seen as impractical until Norway was liberated.

I have no idea if this could have been pulled off. The US Army officers who laid it all out (Eisenhower was one of them) gave it some serious thought.

These V Plans went through several versions. A summary of one from 1941 can be seen at this link:

HyperWar: An Unknown Future and A Doubtful Present [Chapter 4]