[btilly]

Just line up the incentives.

For example require the company bringing the worker in to post a bond, make it trivial for the imported worker to switch companies, and make the original company to pay the difference between what the worker's salary winds up being and what their new salary is after 2 years if they can't hold on to said worker.

If you're a company that really needs that skill, really can't hire it, and is paying above market wages, then this will not slow your hiring. But if you're trying to hire below market, it would backfire badly on you.