Just support the fork on a block of wood with maybe a towel wrapped out it at the crotch. You don't have to push the star nut in very far at all. Rapid taps with a medium hammer will work better than slow taps with a heavy hammer. If you are worried about the start nut going crooked screw a bolt into it to hold it straight and hit the end of the bolt.

Don't be too scared. Carbon fiber is strong.

Don in Austin