You can use a relay from an alarm to startup the PC.
A remote starter is another alternative.
Yes, it's been done. Search the forums.
Ive been toying with the idea of using a remote like the one you would use for fog lights or other accessories to boot my carpc from inside the house.
I think it would make things easier when transfering files from my home pc, i wouldnt have to actually go outside to get things started.
Has anyone ever done this and if not does anyone have any ideas on how to get it done?