You can use an aquarium safe two part epoxy or (I prefer) Superglue GEL. Regular superglue will just make a mess. Also, you can inject the aiptasia carefully with your prefered method (I prefer vinegar) and it should be able to kill it quickly with little or no harm to your zoanthids. In fact, I did this just two days ago with my wife's pink protopalythoas. They were all open the next day and the aiptasia was dead.