This is an awesome question.
Unfortunately, I have no idea ... I can imagine storing something in each user's custom folder and comparing it to the MAC address. My suspicion is that you'd want to use something compiled, maybe Java, to manage the licensing logic, but that quickly moves beyond my experience/training.
Our experiences with the new (6.0 and above) Arbortext licensing suggest you will need to be prepared to deal with the fact that MACs may not always be enabled/available to check.
Your best bet, if you don't get a satisfactory answer to this question here, is to join the Adepters mailing list where lots and lots of Arbortext users, admins, and developers hang out 24/7/365. Information on joining that list (as well as pointers to lots of other Arbortext resources) can be found here:
http://blog.single-sourcing.com/top-arbortext-resources
See also:
http://www.single-sourcing.com/company/social.html
Good luck!
