I do the Same thing but now that I have 3 gtx 480s I want to cool the case even more. I don't want to water cool my cards. It makes me nervous. The only water cooler I have is the corsair h 50 which will never break. I'm sure many people will disagree with me but if anyone knows of a case air conditioner let me know.
the only successful air conditioner mod i have ever seen was done by a gentleman who had AC and freon certs. He was using the freon itself as a coolant and had like a hybrid ac/liquid cooling setup. it was pretty bitchin. I think it warmed up to -22 F at full load. but freon is nasty stuff and super bad for the environment, so I wouldnt go messing about lightly. I think you should get the mineral oil pc case/tank thing and use that