Allow regular user to unlock screensaver locked computer

We have the problem that in a multiuser environment users either lock their computers, or have the screensaver automatically lock it, and leave the workstation. As a result, nobody else can use that computer. By default, only the current user or an adminstrator can unlock the computer. I would like to allow select users who don't have administrator access to unlock the computer.

Is there a group policy or Windows Security setting that would allow some of my users (i.e. non administators) to unlock a workstation?

So far all I can find is a third party application ( Unlock Administrator http://www.e-motional.com/ULAdmin.htm ) This program seems to do the trick but I obviously would prefer to do this through GP.

Note: I don't want to let just anyone to unlock the computer - I want to be able to select only some users.

Any suggestions?