I came up with an idea....
You could keep a bottle of nitrogen next to the system at all times and keep pressure on the system from the bottle. Of course you would need to "charge" the system first by removing all the O2 + humidity by using a vacuum and replace the vacuum with nitrogen gas. Once the system is "charged" with nitrogen, you use the bottle to keep a pressure on the system. If any gas is released due to a slow leak, the bottle will keep a constant pressure on the system. When the bottle gets low (hopefully not too quickly), refill it and keep going.
Just imagine having a N2 tank attached to the side of your computer....you could claim that its Nitrous powered..
You could use a heat exchanger to cool the nitrogen gas sealed inside the case and cool the exchanger with an outside source. The water cooling system would HAVE to be completely sealed inside the case though or else any humidity would immediately collect on any pelts or cooler surfaces due to being a different molecule inside the almost pure nitrogen environment.
This could be done but would require A LOT more maintenance than a standard H2O cooled system......
BTW it would be best to have an external box with all your cable hookups.