This seems like a pretty easy way to get 12v DC for coin door lights, a trackball light, or whatever you need it for (and to get 5v and 7v DC as well).
http://www.xoxide.com/pci-power-bracket.htmlYou could always cut the wires on the second 12v plug and run it to your power switch header on your motherboard so you could mount a power switch on your cab).
I made something like this for my cabinet a few months ago. I took an old PCI slot blanking card and drilled to holes in it, put two k-size DC power jacks (Radioshack number 274-1565) in it, wired one set up to 12v on a power supply header, and the other to a spare plug for the prongs on the motherboard for the power supply. So then I could connect the lights and a button each to a matching k-size plug (Radioshack number 274-1569). This seemed like one of the cleanest ways to do it.
Sorry if this isn't the best place for this message or if somebody's already mentioned it.