Thanks for the replies, I thought about a powerhead aimed at them but that might tick off the other nearby corals. I will try to slice off and save what I can and paste the rest. Will the shrooms I paste just slowly die or let go right away? Do I try to inject them right in the mouth or at the base?
I actually don't mind shrooms at all, as long as they are on their own rock and not able to spread onto the main rockwork (like what's happened to me in this case

)
If anyone wants some shrooms PM me, I have quite a few in my nano that are ready to go now. Whatever I save from my removal attempts will go in the nano too.