I took a 4 inch piece of 1 1/2" inside diameter vinyl drain tubing from Home Depot and wedged it onto the end of the handle. I then cut a piece and wedged it onto the wheel. I had to notch it a bit around the on/off switch and had to build up the wheel on the controller with some tape to make it fit. 1 1/4" tubing would work better on the wheel and you wouldn't have to build up the wheel.
Works great. I can actually drive the car and my hand doesn't hurt. Very comfortable. You do have to put your finger to the outside of the trigger instead of in it to get full throttle travel.