Lugged carbon frame repair
It should be possible to repair the frame, the big question is whether you'll be able to find a replacement tube or will you have to make it yourself. Making the tube isn't hard, it's just messy.

The repair will involve cutting out the damaged tube, working out what else (if anything) is damaged, and paying careful attention to the other tubes. Then once you're clear on exactly what needs to be done (and that the person paying for it is happy with the price) you start. This may end up  cutting an undamaged tube so that the new tubes can be fitted, depending on just how rigid the frame is (it should not be that rigid unless you have a very short tube)


ideally dissolve the glue that holds the tube ends into the frame and pull the two tube ends out.
if not, cut/grind/scrape them out
clean up the lugs
insert new tube dry and make sure the frame is exactly true in the jig
pre-coat the lugs with glue
coat the tube ends with glue
insert new tube
carefully make one last check that everything is true and correct
wait :)


I would be tempted to use a slightly extra thick tube to get a little more strength, since you broke the last one. But that's a path that can lead you to completely rebuilding the frame.