I have thought about this some, put the reservoir and radiator in the freezer (just make sure it doesn't freeze ) and then run the tubing into your case and cool your proc/video card/s
You don't think -200 degrees isn't a "Freezer"? You would first need a custom made igloo to hold everything in however. As you were saying a cpu can run at -40. How about a -200 "ice box"?