The problem is that whatever we do is going to be unhistorical - purely a game device. Personally, I think we should accept that, tell the players in the FAQ why we've done it, and then maybe have some fun with it.
Assuming we use tag U19 for the newly created country, we've got to call it
something - so which would people prefer to see in a report?
1) Soviet Russia has allied with ___User Defined
2) Soviet Russia has allied with U19
3) Soviet Russia has allied with Amchitka
4) Soviet Russia has allied with The International Communist Conspiracy
Vote!!
As for the island to use, I suggested Amchitka because the USA has three island provinces in that area, so they can lose one of them without much effect on the game. Russia, on the other hand, only has one up there, so there's an ever-so-slight, vague possibility that giving it to another country might affect the strategic balance of the game.
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Chile has two islands, but as a really small country losing one province would have a proportionately greater effect on it.
[Edit]Plus, most WW2 scholars will have heard of Attu and Kiska because of the Japanese occupation, but I doubt that anyone but a native Aleut or really good pub quiz contestant will have heard of Amchitka before.