I get a flatened "scoopula" type thing and dig out the rock right under their foot. Sometimes you will see their mesenterial filaments if you tear the foot but give them some rubble to reattach to in a low flow area (I use a glass beaker in a low flow zone so they cant fly away) for about 3 weeks. I have about 50/50 luck with gluing them, some will slime up too much, some wont. Then you can transplant, if you will.
Note: most mushrooms, if you leave a piece of their base, they will regrow wherever that foot is.