You do realize it is almost impossible because keys are already mapped to do other things. It would have been there long ago if it were not for this issue.
HiTech
Why not have the game enter into a different 'mode' when you're in the hanger so that these hotkeys can be used for plane selection? We can have different modes for vehicles and CM eye, etc. Can this be applied to the hanger as well? You have to press a button to enter the hanger as far as I can remember, so why not have that button set a true value for whether you're in the hanger or not and then any of the commands to exit or start flying set the bool to false.
Just a shot in the dark, I'm clueless as to the plausibility of implementing this into the real code.
But this sounds like something you guys have probably already thought of so there's most likely a reason why it can't be done, haha.