I haven't fragged those before, but they probably peel off.
Wearing glasses!, use a butter knife or something to try to peel them off of the rock from the bottom.
Once you have a big enough piece pulled off use scissors to cut between the polyps and remove what you want.
Hope it helps, I think there is a frag forumn on reefcentral's main page.
Be sure to use safety equipment, they have palytoxin that is very dangerous if it gets ingested or into your bloodstream via cut/scratch etc.