It seems like a chicken and egg problem- there's no adjustment or category in USA Cycling for handicapped riders, so few of them compete, so there doesn't seem like a need for any adjustment.
Maybe the solution is to work with some other organization, perhaps one that caters to handicapped athletes? Providing a venue will encourage more atheletes to compete, and that will encourage USA Cycling to do something.
The USA Cycling national ranking is useless for everyone a this point since many races or districts don't bother to send in their results.