take another rock and set it so its practically onbeside the shroom blocking its light and it will move up ward and stick to the rock then just pull apart the rocks whatever is stuck to the rock usually grows into a new shroom, this method has about a 90% success rate for me. the shroom you tear will shock and look bad for a while but mine always recover, I would reccomend cutting them with a razor or scalple since its your friends rock. plus clean cuts heal better than tears do. I'm sure some one else here has fragged them,.. LOL usually they frag them selves like rabbits.