I'm way over my head here but how hard would it be to design a small circuit that when it senses power off, a small memory chip would send the Tsshutdn command via serial port (or USB?????) and if the Bios had the option, wake on ring?
Seems like a breadboard would be cheap enoug.
I know this might be simplistic and possibly covered before but I searched
on "Tsshutdn" and got no hits.
