You can fab up a holder out of an old steel plate, just weld a 1/2" rod to it,bent 90 degrees, and hold the clutch hub with it.
Or, use and air wrencc and just blast it off.
Or, buy the motion pro universal clutch hub holder. It looks like a vice grips with the jaws bent at a 90.
There used to be and old Kent Moore Yamaha style that was aluminum but I haven't seen those for about 15 years, I wish I had one.