Lyn, you can just use a razor blade to cut between the polyps and slice under them to separate from the plug. Then glue the loose polyps to another plug or a rock.
I wouldn't use a dremel on zoas due to aerosolizing nasty zoa compounds.
Depending on the type of plug, you can also cut or crack the plug with fragging shears. If you have the hard ceramic plugs, you can partially score through them from underneath and split them apart with shears.