It's important to communicate. Assuming you know when he's on your wheel, he needs to make it clear if he loses you. It's his responsibility to realize when he's in trouble, and yours to respond accordingly.

The way it worked best for my team is to pick a 1st string and 2nd string sprinter. The 1st string gets on the 2nd string wheel, and the 2nd string just works it like any normal sprint, with a slight tendency to go early if it looks plausible. This way, the leadout guy is pretty fresh just from moving from wheel to wheel. He ends up going at a reasonable time, but slightly earlier, and leaves the 1st string sprinter sitting pretty.

The traditional leadout trains seem like a pretty big investment considering how easily they're toppled by guys like McEwan or Bettini.

My favorite solo sprint strategy is to get on the guy's wheel who would win if I wasn't there. If you've got a 2nd string sprinter who fits that description, you're really rockin' a leadout.