Well, what I do is just stick all of the unused PSU cables into the unused CD/DVD bays. Seems to work fine enough seeing that my DVD-RAM doesn't need much cooling.
either that or get a good modular power supply.
I do the same too, but I've been toying with the idea of getting a nice modular PSU.
As for now, stakicng cables in unused bays and zipties are doing the trick.