An IFC article about Matt Damon's cameos in various films gives us a little more information about J. Todd Anderson, aka Bachelor #3. He's a storyboard artist who had worked on O Brother Where Art Thou, which Clooney co-starred in -- in fact he seems to be the Coen brothers go-to storyboard artist on films from Raising Arizona to Burn After Reading. He worked on storyboards for Confessions of a Dangerous Mind, but apparently Clooney decided he would also be a perfect fit for the small role up against Pitt and Damon. The two better-known actors had co-starred with Clooney the previous year in Ocean's Eleven. The clip below is less than 40 seconds long, but a very funny use of cameos, without going over the top.
P.S. I hadn't realized that the boyhood Chuck Barris in this 2002 film is played by Michael Cera. I may have to watch the whole movie again -- Sam Rockwell is wonderful as the grown-up Barris, and Clooney gave himself a fun supporting role, too.
P.P.S. This post was in honor of the news that Pitt and Damon will be re-teaming to lend their voices to Happy Feet 2.