Another option would be to get an "extra" power supply into the system to power the watercooling or almost anything else (even the system itself). Its called a pico-PSU:
http://www.ncix.com/products/index.p...ure=Mini%2DBox
Could be a good option to help you out!
Edit: Looks like that one is no longer available... but you should be able to find/order a similar one for most computer stores.