I've donee something similar too, with with a script that'd continually poll a website upon user login and findmymac. The only issue is a firewall on the route

I've donee something similar too, with with a script that'd continually poll a website upon user login and findmymac. The only issue is a firewall on the router side, but, that's a highly targeted attack then. You also can't set a bootup/EFI password.