Yeah, this was why he was in that ABC teaser (with Patrick Dempsey, Courtney Cox, ect) a while back. Alot of people speculated that he was returning to Lost after he made a reference to his own character stating "actually I wasn't" after Ed O'neill told him "Your so dead" but it turned out just to be a tease.

The article with the video can be found below.
http://tv.ign.com/articles/992/992341p1.html

Yes, Dominic Monaghan will be appearing on a new show called Flashforward, starting 24th September, 2009 =)

Yes. D.M. will be in next week's episode of Flashforward, according to the "scenes from next week" at the end of this week's ep.

yes charlie is in this show but so is juliette and i have an internet rumor that the actress playing libby will also be in flashforward guess we have to wait and see