Find a natural enemy of the shrooms, like Galaxia, and corral/contain it. Then get a syringe with kalk paste and inject them. It will kill the majority but they will come back...
Or trade the rock with fellow reefers that want them. They get rock with shrooms you get clean rock. I did this with Metallic green polyps when they got out of control. I know it made a lot on this board happy with the trades.