first, their is a number of ways to do it. you can cut the rock up that they are on. or you can cut the base of each individual polyp. after you cut the polyp at the base, super glue it to a small shell, or LR rubble. then in time, it will open back up and contiunue to grow!
Saltwater Aquarium Corals for Marine Reef Aquariums: Starburst Polyp
read like half way down the page.