Try this... just as a test... take 1 shroom, with an exacto cut into equal halves.Get a shot glass and put a piece of rock/rubble in it then put a half in there and set it out of direct water floe in the tank on the sand... should attach within 1 week. Next, take the second half and drive a wooden toothpick through it. Now, on the base side of the shroom where the tip of the toothpic has come through, place a dab of gel super glue and set in place on the LR(shrooms tend to prefer like less water flow and a lower light). Now, clip off the remaining toothpic at about 1/2" above the shroom... you're done. Given the scenario that your water quality is at the shrooms prefered levels and your lighting is sufficient, your shrooms should heal rather quickly and begin taking their rounder shape back on. BTW, I've performed cuttings of 4 out of 1 shroom on several occassions with the same success. (IMO) though, confidence in what your doing is very desirable so try this halving test, first.

   Good fraggin', Jason