There isn't right now, and not sure if it's even possible. When a comment is posted to Facebook, it gets a special format that Facebook automatically dictates. The comments are threaded (unlike a forum), and there wouldn't be a way to keep the comments in the forum synched up directly with Facebook. Similarly, if someone responds in Facebook, it could be difficult to push that comment back into your forum in a way that makes sense.
With that said, in the 4.1 release (4.0 is coming out in the next few weeks), we're currently planning to focus more on commenting and implementing other ways that comments can be posted to walls and such, as well as more flexibility of the looks of comments and other things. It's still in the planning stages, and there's always the chance that Facebook could change what's available to us. Hopefully, if everything goes to plan though, the 4.1 release (a few months away) will give you more flexibility with Facebook Comments and hit your needs.
I know that wasn't the exact answer you were looking for, but hopefully it helps explains what is, and isn't possible.
Thanks,
Alex
Comments on content in agora forum AND facebook.
