Hi Gary, I am intrested in replies to this question and thought someone might come along.
However a couple of things spring to mind, for a possible test and a cheapish get out.
If possible wrap the drive shaft with an elastic band to see if this gets around the problem, there should be more 'grip'.
It may be possible to improve the edge of the rubber wheel by sticking a strip of cycle inner tube around it. Watch out for rotation at the scarfed joint. Contact adhesive should hold well, at least in the short term.
I made a stropping device with the leather tyred wheel running directly on the motor shaft. I was expecting quite a bit of slippage, this has only happened once wnd that was with a very heavy load. Me trying to be too heavy handed.
HTH xy/
p.s. Sorry I don't have the Tormek, all the above is guesswork.