As part of the pre-Oscar publicity push for
The Social Network, a making-of featurette that's included on the DVD release is available for viewing on the IMDb web site. It's called
How Did They Ever Make a Facebook Movie? Here's the link:
http://www.imdb.com/title/tt1285016/videogallery/content_type-Featurette?sort=6I've not watched all of it, so I can't comment on whether he appears in any of the other portions, but he is definitely in the segment labeled "Part Four--The Lot," which shows the filming of the deposition scenes and discusses how Fincher shot hundreds of takes.
Spoiler alert: The shooting of the final scene is included in this segment. The portion with Selby begins around 16:07 and ends around 20:00.