completely crazy idea, but since many ghosts seem to suck the warmth out of the areas they occupy, or at least create pillars of cold air, presumably feeding on the heat energy perhaps it might be possible to encourage the to do this as a form of air conditioning.
Maybe it might even be possible to convince the undead to help counteract global warming.
Is you Troll?
aww man, that's a great idea! how would you get them horizontal though so they might create streaks of cool air? also, how would you keep them semi-stationary?lol