This is an issue I wish the game by vanilla would just let you turn over control of territory to your allies as this happened a lot between Germany and Italy. I have allowed enemies forces to capture a territory just so I can turn it over to another.
thats y i like to have build transports at least 2 on the first turn if for no other reason then to reinforce norway if sealion doesnt happen and yes the ic in the ukraine is very nice if u do decide to go for russia