get a clean razor, and just chop the head right off. then take that and cut it into 4 pieces like a pie. rinse the pieces with water from your tank and put them in a tupperware with some rubble in a low flow area of your tank. within a week or two they will attach. viola! the base that you cut the head off will grow back and each piece will grow into a new mushroom.
it sounds brutal, but i swear to god, shrooms are bulletproof.