You don't need a power switch. We have the BIOS to auto-power-on upon power failure, so you just flip the PSU switch off and then on again, and the MB turns itself on.

You will need to turn it on once, before you configure the BIOS settings, but that's pretty easy to do, using a switch from an old PC case, or just simply touching the two power on pins in the MB header together with something metal, like a screwdriver or a metal pen tip.