What about using the user profile to control how maney times they can sign.
If you do CHGUSRPRFand change Limit device sessions . . . . . . . . . . : *YES.
will this help.
NO Missing a lot of information about your security model but …
Can you limit concurrent sessions per machine by IP or MAC address?
The other option I can think of is restricting CL access to help circumvent the second session.