I have these 2 and just use a razor then rubber band the frag to rubble for 10 days.
https://reefbuilders.com/2010/12/15/blue-photo-sponge-collospongia-auris/#
http://www.liveaquaria.com/product/prod_display.cfm?c=597+2341+2512+3540&pcatid=3540
Never lost a frag removing it from the water to cut and mount