AFAIK, only the currently logged in users or Administrators can unlock a screen saver state PC.
Quite honestly, that's a rough situation as it is because if anyone besides the user logs in, it will force a logoff and then lose any open work.
In my humble opinion, anyone with the need
to unlock a PC when it is locked by a screen saver, should have some type of Administrative rights to the machine, or a generic Administrative account they can do to perform the unlock. Otherwise, what are they really doing there?
If, say the scenario comes up that this is a shared PC, and the general users who use it swap in and out and say the previous user locks the PC via the screensaver and forgets to logoff - and then the next user who comes along can't log them off because they aren't an admin, that's a bit different and gives you two options....
Have an administrator use the remote shutdown command, which is something like this....
shutdown.exe -m \\computername
-t xx -r (something like that, and the "xx" is time interval before the shutdown goes)
Either that, or install this little utility -
It will actually log the user off after a pre-determined amount of inactivity.
Other than that, perhaps provide more details as to what you are trying to accomplish maybe?
Other suggestions would be interesting for me to know as well.