Okay, this is going to get a little weird but it's a thought: remember the Bone Phone in the '70s? It worked by vibrating your collarbone, and then there are those lollipop holders that play music by vibrating your teeth. These all work by something called bone conduction. There are some new headphones by Vonia that work by sending sound through your skull rather than through your ears. I have no idea if this would work as a monitor but if did then it would have the advantage of allowing you to hear all other room ambient sounds while hearing what comes through the headphones at the same time. Great for listening to music at your next Star Trek convention with! In case you want to read more:
http://grabit.co.za/vonia/index.html