Ask HN: How should we approach remote code interviews?

We've nearly exhausted local candidates and are starting to look at remote interviewing. How do other companies approach this? We've got a small programming problem that we have people do if they pass a phone interview, but I sure do miss the ability to put them up on the board and see how they work out a problem.

Flying the person in for a final interview is an option, but are there other screen sharing strategies or something like that to see how people approach an on the spot problem?