What I have seen done before is the use of a standard radio by one hand from an amputee. You would have to practice alot, cause you used your thumb only for steering and regular finger for throttle/brake, and the final 3 fingers to hold on to the transmitter.

The other thing you can do, is to make a chair with a foot pedal wire extender to control the throttle/brake and make a stand that holds the transmitter so that your one your free hand can control the steering. Its pretty duable, but would take some building and setup time. I once used some one else's custom chair control at a RC track in phoenix AZ and it was very neat and very cool. Took me like five laps to get the hang of it, but I was using both hands to steer sitting down and my feet for gas/brake...it was awkward to drive a 1st person view configuration to a 3rd person view from the drivers stand. I cant remember the manufacture name off the top of my head, but it was a European company of sorts