Well the obvious way is to make them feel unhappy, that they aren't wanted or they're in the way. If they have abilities then you arrange to prevent them being useful in those areas and undermine them to lose confidence.
What if that didn't work? Well, you can make them a better offer.
I've just seen some jobs advertised over near Cambridge, with a really interesting company that might be a lot of fun to work for. They've been doing good and innovative things in the industry, and with my background I'd fit right in. A regular salary wouldn't do any harm too.
But I'm quite sure that, for the moment, it's not what I'm called to do. It's not *really* tempting, but it did make me stop and think for a moment what it might be like to relocate somewhere else without responsibilities and able to re-start relationships with a blank slate and a good reason for being there. Actually it would probably be a bucketload of hard work, but when you dream everything looks easy.