If you want to get rid of the problem of having no live sockets, just add in a second power strip (but make it's just a cheapo regular one). The cord for that strip can plug into the wall, and then the USB strip and the computer can both plug into the second power strip. So you get zap protection for the pc and only one cord out the back.
Even better yet, I would consider adding a UPS rather than a regular power strip. They have an APC on sale at CompUSA right now for like $50 after rebate (or something like that). The reason I mention this is because you won't be the only person using your machine. Other stupid people will just flick the switch off when they are done with it, and if you're using Windows you may never get booted back up again. (Or if your'e using an arcade monitor you may lose video settings or any number of other possible problems.) I only mention this because I've had those kind of problems before. I believe a MAME machine to be as hard to break as a regular arcade machine in every aspect (including power).
I've got a couple of other ideas underway for out-of-the-box power switching solutions, but I need to test them out first. I'm still in the process of building mine. I'll post back when I get some results (and I still need a web page).
I reeeeeally hate chopping up good hardware (arcade or PC) if I dont' have to. That goes for keyboard hacks, pc power switch hacks, etc. I'd break open a power strip, though. They're $10 and just a bank of wiring anyways... Rewiring a UPS wouldn't hurt my feelings either.