I have recently encountered this very problem, for my son's PPL(H).
Although he has some experience in piston helicopters, I wanted him to train in our own turbine, with our own very experienced instructor, through a registered facility at a fully equipped training airfield.
I did get a 'helpful' reply from the CAA, but their solution was that we should use a TRTO with only (literally) a few hours experience on the type, rather than the registered facility which had thousands of hours experience on type.