Converting to PS/2, probably not. It's a pretty rigid (read: slow and dumb) standard, with no provision to carry a "power on" signal. One of the four pins for ADB is specifically earmarked for that purpose.

I keep hearing that PS/2 is at death's door, and yet I still see PCs roll out of factories with the typical green and purple ports.

Guess they didn't get the memo.

If you convert to USB, you could theoretically do it... I think... but only with a fair amount of firmware (BIOS) and hardware (power switch/header) hacking.