I 3D print quite a bit! I've been wanting to incorporate carbon fiber into some of my prints for a while now. One thing I've been thinking about doing is adding in some carbon fiber stringers internally to the prints. I think the best way to do this is to make a void in the 3D model for the stringer, print up to the top layer of the void, add the stringer, and resume the print.
I've also been wanting to try out carbon fiber infused filament, but I hear it's rather rough on nozzles. Have you tried any of the CF filaments yet?