Well it took me a while, but I finally got all the parts, pulled out my soldering iron, and put everything together. I got the PSU I linked to in my last post here. I had to buy a 15P-C19 power cable, since I'm running this on a standard 110V outlet and didn't have the right cord for it, but that was cheap enough. I could easily transition to a 220V outlet and get A) a bit more efficiency and B) more power out of this. It's only rated for 900W on a 110V input, but can handle up to 1300W on a 220V input.
For a switch, I took it apart, and routed a servo extension cable thru the inside, and out a crack in the case. One end is hooked up to the 3 pins that power the device, and the other end is soldered to a simple rocker switch. I could have bypassed this and just run it ON all the time, but I liked the idea of having an OFF switch that wasn't called "yank-the-cord".
I then soldered all 6 wires of a PCIe cable to the 12V and ground leads. It's only about 11-12", which isn't the longest cable in the world, but it works. I've only got 1 attached for now, but that's enough to test it with my Little Single for now. Soldering 3 of those wires into each clamp was a PITA, at least for me who's basically a nub when it comes to soldering. This thing has enough juice to power up to 8 PCIe 6pin connectors, but that means I'd have to figure out a way to fit 6 wires per clamp, which could get interesting.
Right now, the only thing stopping me from running 4 SC Singles on it are A) getting the rest of my hardware from BFL, B) fitting and soldering 8 PCIe cables (or all 48 wires) into the 8 clamps, and C) moving all the hardware onto a tray on a rack and hooking it up to a 220V line.
Word of advise: These things are loud! There are 2 fans inside, and they must spin pretty fast, as there's a good amount of air moving thru it, and it uses ~60W with nothing plugged into it! I guess you can put a resistor in there to slow the fans down, but I haven't done that yet. I plan on putting this in a location where noise is a non-issue, so I don't really care.
My Little Single was using ~120W with the stock brick, and now this PSU and the Little Single are using ~215W. Minus the 60W for the fans, it looks like this is using 155W, so I think it's actually less efficient than the stock power brick. Does that sound right? I don't know the numbers of either, so I can't say. It puts out 12.56V on idle, and 12.49V with the Little Single running. Not bad, and I don't think it will even drop below 12V when running under full load. Here's a pic of it running the Little Single:
Hope this helps anyone else, and I'd encourage you to try it. If you've got an isolated location where you don't care about noise, and you want to consolidate your power supplies, it's a MUCH cheaper alternative to buying an ATX one and powering it that way. I have ~$40 into it so far, but I have to buy a few more cables to rip apart and solder onto it. All said and done it'll cost me less than $60.