That's one of my favorite lines as well--one of the reasons I'm sorry to relinquish the story.

I suppose it could be a missing scene, but it sets up expectations which the show never lives up to. It's not entirely impossible that Sark was in contact with Jack, but at this stage it appears very, very unlikely. (I did have few lines of a post-Mexico scene to add to this, but it just wasn't going to work out--it would have required an enormous edifice of plot to support it.)