Micro Max cordless rotary-tool kit, by Dremel, 8 volt, $89, homedepot.comDiamond-coated twist drill bit (#56), by Eurotool, $6, metalliferous.com
Place sponge in container. Fill with enough water to just cover sponge. (The water will keep the drill from overheating and the shell from cracking.)
Set shell on sponge, top-side down, and hold securely with your fingers, as shown. Keeping edges barely submerged, slowly drill through shell.