Perhaps the main thing such a society could do is maintain a website with data about employers that have non-compete clauses in their employment contracts, and the extent to which they try to enforce them (like Chilling Effects, but for employers).
If prospective hires for such companies knew that they would be seen as damaged goods on the employment market as a result of working for a certain company, it would influence their choice of employers, especially in the common scenario of having a few offers to choose between and not having much else to separate them with.
If prospective hires for such companies knew that they would be seen as damaged goods on the employment market as a result of working for a certain company, it would influence their choice of employers, especially in the common scenario of having a few offers to choose between and not having much else to separate them with.