Yes, it has been done. I remember seeing several experiments where this one guy modified a foam cooler to house a barebones setup submerged in the stuff. Then he went using dry ice pellets and a waterblock with liquid nitrogen cooling. Had some pretty good results, but the price definately puts it out of reach of most people... Flourinert is something like $500 a gallon. Here are the links to the Flourinert projects. They seem to be down for me but then again I am at work and a lot of things on the 'Net don't work right from here...
http://www.octools.com/articles/subm...ubmersion.html
AND
http://www.octools.com/articles/subm...bmersion2.html