You may be the first to do it, I'm getting one this weekend and if you don't have it figured out by then I can post it. Just a matter of finding the right chips with a meter. I you have a meter you could locate them by youself. I can post a pic of where to check if you have a meter.
It's actually very simple, with the sys up and running, connect your black lead to gound (case chasis) ant then probe the center terminal of the mosfets with the red lead to find the one's with the +5v rail. Then just solder your wires to the ones that are +5v.
Not sure when I'll have mine done, may not do it right away but I could locate the right ones for you.
First I would check the +5v at the mosfets to see if you are getting a voltage drop there. It is possible that the readings come from around the atx plug and wont show the drop. If the voltage isn't dropping at the mosfets, it wouldn't be worth doing IMO. Check the voltage at the atx connector and at the masfets, I believe the manual shows the pinout of the atx plug, so you can find your 5v lines easier.
I put a picture in this thread of which mosfet and where on it to put a dedicated +5V conductor. That will reduce the voltage drop occurring across the ATX connector. In the picture, I indicated that actual tab of the mosfet, but the center pin (the one that is clipped short) is the same connection if you'd rather solder to it. Good Luck