| I seem to remember hearing about bass necks that were wrapped inside a carbon-fiber tube for strength, with a fingerboard glued on top. The general idea is that you slip the tube over the already-shaped neck and wet it out with epoxy, put some heat-shrink tubing over it, point a heat gun at it and pull on the ends to shrink the carbon-fiber tube around the neck.
I know you can buy the carbon biaxial sleeve and matching heat-shrink tubing at Soller Composites. Fibreglast has the sleeves, but they're a bit more expensive and I don't know if they have the heat-shrink tubing.
Also, not sure about homemade solid-graphite necks, but I've heard of people buying them. | 
