I built a sort of home-made equivalent to a bridge doctor (no, no relation) to go in a Framus 12-string I had been lent but which was unplayable due to extreme bellying. The Framus had a string-through bolt-on bridge (!) and so neither of the actual bridge doctor versions was going to fit. I clamped a large-ish wood block onto the inside of the top using dowel nuts (think Ikea) and the original holes for the bolt-on bridge. Then a Tee-nut on the blind side of that wood block enabled me to thread a bit of 6mm threaded rod up to push onto the tail block.

I'm sure this bodge is quieter than the guitar was, possibly because of the increased mass in the bridge area. I think my version is probably heavier than a real bridge doctor. I also expected the extra mass to decrease the resonant frequency of the top and so increase bass, but that didn't happen.

The problem was that with the threaded rod pushing and the strings pulling, the bolt on bridge tends to work towards the nut (it doesn't move once it's on so long as you do the clamps up to fart past grunt, it's just hard to get seated accurately).

To avoid filing long oval holes in the top of the Framus, I actually put a bit of shaped metal behind the original saddle to increase the tuning length and the octave is now about right.

It's a bodge. One day I'm going to take it to pieces again and do it right!