MAC host checking is limited to files, processes and ports. So you would need to have some form of an embedded process or perhaps a file that you dumped on the MAC that reflected the version. You could then check against that file.
A periodic process (crontab) owned by root something along the lines of...
uname -r > .hiddenfilesomewhereobtuse
...might do the trick. The problem is that once someone discovers where that is, if they have admin access then they can change it and stop the cron job :-(