I remember reading a post a while back, I am pretty sure it was here, but I can't find it now. Anyways, they suggested using aluminum tubing as a mandrel. After the carbon is all cured and ready packing the tube with dry ice to shrink it. The idea is that since carbon is not as sensitive to hot /cold as the aluminum the mandrel would shrink enough to slide right out of the new carbon tube. I wish I could remember what thread that was under to credit the idea. Seems like it would work given the properties of the metal versus the carbon.