I suspect that repair shops that specialized in repairing frame bonding on Vitus 979 and similar frames (like I think the now defunct "Guywires" in Canada did), in some way, exposed the unbonded end of the frame tube and cleaned off any old Epoxy glue and corrosion from the tube end and lug socket mechanically, (sanding, Dremel, hones...etc) and used new glue on the joint. It could be that they are able to flex the frame enough to pull the tube end out of the lug socket with some sort of jig without having to further take apart the frame at the other joints. Once one can figure out how to do this exposing the tube ends and lug socket and doing the cleaning, it's only a matter of figuring out what glues to use. I would think that a search in the internet for the strongest epoxy glues one can find, can get you in the ball park of acceptable glues for the application. I would think one can find many more commercially available Epoxies that would be even stronger that what Vitus used back in the 80's....
.....Just my thoughts on how to possibly approach Vitus 979 or Carbone frame repairs.