Mmmmm... The funny to flack offset probably isn't worth it to Stewart and Colbert. They're not news shows and there's not much comedy to draw from the SOPA proceedings. Especially with Ameraca's favorite reality show cramming up the broadcast space.
Their interviews are the real deal. Getting a famous Internet person on to talk about SOPA wouldn't be an unusual thing for either of them.
"Famous Internet Person": I don't know. I would much more prefer some artist, director, politician and not another "internet activist".
Niel DeGrasse Tyson? I don't know his position on SOPA, but I'd imagine he's against it. John Hodgman? He's a writer for Wired, been on Diggnation, Attack of the Show, and TED, and works with Jonathon Coulton. He's got a ton of 'net-cred and is frequently on TDS.
I would much more prefer seeing one of the household names in the "old" media see speak out - some of the more expected opponents like Al Gore, Mc Hammer or Aston Kutcher would give the issue a better face and show that the opponents are not just some people from the internet who want to "to kill our beloved music and movie culture".