Years ago my boys got one of the first sets, and the little one got a new Cars 2 Shake & Go raceway. We have about 6 cars from over the years, and one of the wheel switches on one stopped working. That was the one I thought I would experiment with. It was such an easy mod, it took longer to wait for my soldering iron to heat up.
First open the 6 screws on the bottom. Then solder a wire from the first tab on the wheel switch to the capaciter solder point on the wire that goes into the motor. Line the springs up and screw it back together. Now the switch turns the car on, and if you pick up the car, it stops. The motor noises still work, and if you shake the car, it also still works. The car seems to go faster, so the IR emmiter doesnt always catch the car as it goes by on the older track, but its worth it. I see going through AA's on these cars faster!