This is why I lie awake at night dreaming of in-floor radiant heat. But I digress.
During my working hours, my computer blows hot air out a vent at the top, probably raising the ambient temperature of the room a few degrees. This is nice, but how hard would it be to harness this heat and blow it on my feet instead of up towards the ceiling?
I picture a clear, plastic shroud that snaps around the top corners of an iMac, like one of those vent covers your grandmother used, but much more elegant, and probably hand-extruded in Brooklyn. Perhaps magnets are involved. Combine this shroud with a length of flexible tubing, and a small USB-powered booster fan, and I think this is a winning idea. The tube snakes under the desk with the rest of the cables (and, for that matter, could serve as a cable organizer), and exits at or near the feet.
I've provided the idea and the detailed schematic. Now get to work, Internet!