No problem to make the PSU external... Just build a enclosure to it and connect some wires. But where is the benefit???
You even lose the aktive cooling by the PS3-internal cooler. It doesn't matter to the cooler if it just flows by the power supply or not
Here is a thread in german about a tuned PS3
in German language. Unfortunatelly I don't know which parts are changed within the psu. So nobody who worked with the psu?
I think an optimization might be important for anybody using the PS3 as a BD-player and wants to reach the best quality.