Some Bios' have a turn one feature, for specific times. You might also consider a small timing device, just dropping 12v into the ACC line, as if you were starting your car, to kick the PC on. One final idea is to use a Wireless relay controller. I have one on my car, with 4 channels. Have it hooked to ACC to boot the PC.
The enxt aspect is starting your car. Easiest way would be to get a remote starter kit and hack one of the remotes.