Man, that would suck!!!
Anyway, with a bay res, you would have multiple inputs & outputs:
CrazyPC UV Blue 5.25 inch Bay Reservoir
Was that what you were thinking of? Also, I found a guide on how to make blocks to cool mosfets:
http://www.overclockers.com/tips1104/
When you do it, we need pics!!!
Edit: an easy & ugly way to make your own waterblocks:
http://www.overclockers.com/tips730/
Also, I just had a thought...why water cool your power supply at all if you could buy a fanless one like this:
COOLMAX Black 480W Fanless Switching Power Supply
It wouldn't be real inexpensive, but it would be a lot safer!