I don't think you can do it. I asked this question a few months ago and you couldn't, seems like you should, though.

On OS2008, Orb plays for me just great with no changes. It doesn't matter what the video on your computer is as it is reformatted and streamed in whatever Orb is set to. If you want, you could try changing your Orb settings to stream in Real. Doesn't solve you wish to choose a default program, but your videos may play.