I can picture only two ways to remove the star nut without further damaging the carbon.

1, simply grind the bastard out with a dremel. Highly tedious.

2, fashion a clamp that forces the nut into a cone shape. Possibly painstaking, but I'd consider it first. It could be used on other star nuts.

I guess a possible dealbreaker is the hole in the bottom of the crown being too small to allow a large enough tube inside.