Volunteer when you hear layoffs are coming. Just tell your boss you'd like to be on the list.

They will usually oblige you because you are solving a problem for them (meeting their cut headcount requirements) and they know that if you stay you might leave anyway and if you don't you'll be unhappy.

Heck, if they layoff is a surprise, ask your boss if you can swap with someone else. They often have the flexibility to do that.