usb keyboard start button emulation

I have a Cube's guts taken out and sitting on a table and I'm trying to start it up (unsuccessfully). I'm pretty darn sure that everything is hooked up properly. However, as pointed out on this page, it doesn't work with the power button hooked up, he recommends a usb keyboard with a power button. I don't have one handy at the moment, only the Apple Pro keyboard that came with the Cube. Is there a way to emulate the power button? Does it just short the power pin to ground? I don't want to try and experiment and end up with a bad USB port.