I don't know of a way to do precisely what you're asking, by way of tagging in SM.
About the most effective method I've found for encouraging staff to use the right SSID is simply to make the recommended SSID better suited to their needs, e.g:
Set the Guest SSID to require them to login and re-login every few hours
Apply more rigorous traffic shaping / firewall rules to guest clients
Make the recommended SSID as seamless a signon experience as possible (use Trusted Access, for example?) - and loosen traffic shaping constraints.