I found a video showing Damon Lindelof and Carlton Cuse crashing the Entertainment Weekly (Jeff “Doc” Jensen and Dan Snierson) LOST panel, with Carlton wearing a Star Wars stormtrooper costume — supplied by a fan! — and Damon, a Dharma jumpsuit.
Here’s Carlton walking down the hall in his costume:
Videos via LOST in Comics, a blog written by fan artist JJ Harrison, whose poster was honored by Damon at the panel:
The LOST in Comics post has a description of the event along with pictures of Carlton putting on his stormtrooper costume backstage and then sitting, in costume, in the audience of the LOST panel, with no one around him realizing who he was.
In case you haven’t yet seen the “deleted” Season 1 finale scene Darlton showed at Comic-Con, here it is again: