I posted an article, earlier today, regarding slate mosaic tiles I put in my 76 Sovereign
. When I encountered the raised toilet problem you mention, I found that it wasn't much of a real issue at all. After I stripped out all the old carpet (yes, some previous owner actully installed wall to wall carpet) and removed the toilet from my bath, I noticed that the flange that connects the toilet to the black water tank can be unscrewed after you remove the 6 screws in the plywood. I made a special "wrench", to unscrew it, by fastening together two pieces of wood. One small piece just fit into the slot (approx .5 x 5 inches) and the other was about 2x2x12 to provide necessary leverage. After I laid my 3/8 inch worth of tile and thinset, I simply screwed the flange back onto the black water tank. Originally, the threads were long enough to protrude into the tank an extra 1/4 inch; however, after my slate floor was laid there was still a lot of thread available to keep everything secure. I then just put a new foam gasket, from HD, on the toilet and it went together perfectly. I won't use a wax gasket in a TT. I think that the motion and jarring that these toilets get in a TT would cause them to eventually leak.