I'm almost positive that this isn't what it seems. So before I start with my idea, I just want to say that I loved Peace Talks. It seems like people here don't understand that the book isn't supposed to be standalone. Jim said himself that it was either two books or one really expensive big book. With that in mind this half book was a great read. Now, onto my speculation. 

Thomas only gets to say "J" after he gets beaten up. Both times he says it he gets interrupted before he can finish, or simply is too weak to do so. I don't think Thomas is trying to say Justine. The only people I could think of are Johnny Marcone, Jade Court, and Justin Dumorne. Anybody have any idea of what Thomas was trying to say?