Lots of good options for G1 builds, but here are my personal thoughts. Two bombers can help Sea Lion in the following way:
Clean up residual ships on G2 to prevent ship blocks Bomb London on G2, doing ~9 points of additional damage to the factory which reduces the number of infantry built on UK2. Join in on the London raid on G3, contributing 8 more attack power (equivalent of 2 transports loaded with infantry + art) for approximately the same purchase cost Attack the Russian response on G4-G5; bomb Russian factories along the front. Attack the US Navy trying to liberate UK on G4-G10ishAdditionally the two bombers are quite useful to bomb Moscow and support a Barbarosa if Sea Lion is not an option. It is not as optimal of a build of 6 art + 2 inf for marching into Russia, but still is very beneficial.
:-D