i'm currently in the process of attempting this. (on a slim)
i've worked out how to take a link from the front left usb port. but then its not a true usb port more like just an extension of the one on the front. effectively it will be just moving the front left one to the rear and then blocking up the front left port.
I intend to run a laptop cooler from it that has 3 usb ports built in. (Front port would become unusable hence blocked off) this will sit underneath the PS3 and glow blue., with the 3 ports being at the rear out of site, 1 for EXT hd 1 for controller cable, and 1 spare.
leaving the front right usb port totally intact for usb stick FW updates etc.
if all gos well and i don't blow anything up. i'll post step by step pics and a guide as soon as its ran for a few weeks without problems.