A scooter is automatic so with one of them you just need a throttle. But the clutch would probably not be very happy pushing a car around.
I would suggest using RC car controls to operate everything on the bike. That way you could just unplug the harness and the bike is free and still mostly normal looking. 3 servos to work it all. one for the throttle using a small lamp pull chain type connection to the carb so it doesn't interfere with the normal throttle. Need one for the shifter up and down. It would most likely have to be unhooked from the shifter arm when riding to keep from breaking it. And a monster servo for the clutch connected similar to the throttle by connecting it on the arm coming out of the engine.
Getting power to the bike would also be helpful so you could put a remote neutral indicator light in the car so you know when you found N and can let the bike just hang on for the ride.
Just some ideas I am tossing out there. I have no idea if it would actually work. But it would be cool to see running
