I sent a package to Lars containing a hot wire ice cutter for him to try out. It consists of a home-made variable power supply (encased in a CD spindle shell) and a 10 inch nichrome wire on a wooden bow. Since receiving it, he has used it for cutting foam but hasn't tried it on ice yet. I'm hoping he will try it in cold temperatures to see if it causes ice to crack.
The CD spindle (with center post removed) turned out to be a great case for the power supply. I used a cheap triac dimmer switch, a transformer salvaged from a useless wall-wart, and a little fuse holder from Radio Shack.