
Visiting a users machine to resolve a help desk ticket is frustrating if that users screen is locked and the user has left for the day, is out to lunch, in a meeting, etc.
To enable an admin to unlock another admins screensaver you simply edit a file on the machine, edit the file: /etc/pam.d/screensaver, changing
account required pam_group.so no_warn group=admin,wheel fail_safe
to
account sufficient pam_group.so no_warn group=admin,wheel fail_safe
You'll need to use a text editor capable of modifying and saving system files; e.g. any CLI editor used with sudo, or a GUI editor like TextWrangler if done in advance. It is not necessary to log out or restart. In fact if you visit a machine that is locked in this way and have SSH access to it you can modify this file and then unlock the screensaver using your admin account.
[crarko adds: I tested this, and it works as described.]