I asked a question similar to this not long ago. I never even found the right wheel for it.

To help with your question: I'm pretty sure that the cone adapter on the starter should be replaced with a car adapter that will properly hold the starting wheel.

2 other points to help you out: The wheels are more often referred to as starting donuts, and they are much more common in 1/10th scale. You might try polling those forums for more info.

Now for me:
Has anyone tried the Sullivan Tiger Drive backplate for a 90 degree starting angle on their buggies?????? I am torn between this and a roto start system.