I checked the BIOS, and this particular board does not support auto on after power outage.
This is going to be a solar powered project, and while the computer needs to be on as much as possible, nobody is going to die if it doesn't. The main issue is that it is going to be located a couple of hours from where I live, so hitting the power button is not practical.
Also, this board has an integrated power supply that is powered by a wall wort, so I can't ground pin 14 of the ATX supply for always on.