Just to make sure I'm understanding you here, you want your computer to turn on whenever you turn your power supply on at the socket? Well anything's possible
Some systems have the ability to power on when you press a certain key on the keyboard. I know on my keyboard there is a wake-up button for this. I've never used it but it might be worth looking at for you and may be the more simple approach for what you're looking to do. Google is your friend.
That would definately work and it may even be easier. My issue is that i built a desk and actually built a pc inside the desk. The top of the desk is plexiglass so you can see all the components on the inside, but the on button i have attached is on the motherboard since i dont have this conected to an actual case with an on/off switch.