With this in mind, we took out the tubes to be replaced by bamboo. Again, we didn't have the technical resources up the rear dropouts well, (if we'd used Misumi Extrusions we would) so we spared the rear triangle. We also spared the seat tube clamp area, so the seat tube would have a nice interface.
The dremel diamond wheel cuts carbon like butter. The other bits won't, so this piece is necessary if you want to do this without a headache. Get goggles and a mask. Cutting is dusty and particulate carbon causes a whole pile of health problems later in your life.