What I don't think you guys understand is that the dry ice evaporates/melts pretty fast.
Quick guesstimate of about 20-30 lbs for a day of usage. Add to that the acetone you need to add to make better contact with the base and your talking a decent chunk of change in expendables alone.
It is not at all practical, and is only even imaginable if your benchmarking.
You would also need to have the motherboard on the horizontal which would either mean no case, or your case laying on it's side on the ground.