you'd be better of making a chiller then.
You have to make blocks for your graka and cpu and stuff to connect your heatpipes to anyway, so you can makewaterblocks too.
instaid of hooking up you heatpipes to a cold plate, put your cold plate in a reservoir and run you 'water' trough it ...
You'll achieve much better temps than with heatpipes, the amount of time and money to put into it would be about the same prolly.
yet you'll still need a powerfull compressor. A modified vapochill or prometia won't handle the charge of a whole system... I think...
anyway, it's a crazy idea indeed
grtz