Yes Nathan Fillion is in Guardians of the Galaxy, but as who?

It's been rumored since James Gunn was announced as the director of Marvel's Guardians of the Galaxy and it's finally been confirmed.

“@STARS_TyranT: Are the rumours true that he has some part in the film?” @nathanfillion has a very small fun cameo he did as a favor to me.
— James Gunn (@JamesGunn) June 21, 2014

Earlier in the week rumors were flying around the net that Fillion was going to be playing Richard Rider, Nova but he already debunked that one.