Sources tell me Bilbo wasn't present when they were shooting the Council scenes - which isn't to say that he couldn't be added in later I suppose, but I doubt it, because Frodo was there at the time.

Also, we've seen many pictures of the Council, and none of them have shown Bilbo. I'm pretty sure the hobbit sitting next to (anticlockwise) Gandalf (or rather his empty seat) in "889.jpg" is Frodo (or rather, his small stand-in) - c.f. 1166 and you'll notice the clothes are the same.

You'd think that if Bilbo was there, he'd be sitting next to Frodo, but you can see from pic 889 that no-one is. Hmm, you know what else is weird? In the trailer (trailer02_49.jpg) where Frodo is standing up, there isn't a chair next to Gandalf at all...