One thing in 4x05 The Constant nagged at me for some reason when I saw it. When Desmond first runs into Faraday at Oxford, he finds him speaking with a student. This student pops out of the background, appearing to be unusually pale, and wearing distinctive glasses with smoked lenses and a conspicuous striped yellow sweater. He looked oddly familiar, but I couldn't place the feeling.
This afternoon my unconscious, which had been working on the problem all night and morning, finally came up with the answer.
He looks a lot like Lost writer and co-executive producer Adam Horowitz. I might be wrong, but the more I mulled it over, the more the two seemed to match. He really looks like his appearance in the "Lost in a Day" extra from the Season 3 DVD set, where he appears with his writing partner Edward Kitsis. Incidentally, if you've noticed Ethan Rom wearing University of Wisconsin sweatshirts, they are likely the reason why, because that is where they met and started writing together.
One detail that argues against this theory is that Horowitz is not credited as a writer for this episode. And like all the writing staff, Horowitz is based in LA, and not in Hawaii where the filming takes place, but as a co-executive producer wouldn't you pull strings to get yourself a work vacation to paradise? Now I'll be looking for Eddie Kitsis in episodes.
I suppose we should just post a query for Gregg Nations at The Fuselage to settle the answer once and for all, but for now I'm willing to go out on a limb and on the record to call this a possible cameo and Easter egg exclusive.
And while we're talking cameos, some users noted Lost executive producer Jack Bender's dog Lulu sitting leashed on a lawn in the scene in Oxford. Maybe the dog is Jacob. Just kidding.