A wiser CAP guru would have to comment, but I believe the problem with a sign and trade is that any signing bonus money combines and moves forward into a single large CAP hit. Kinda the same reason certain players can't really be cut in the early year(s) of a new deal because it creates a pile of dead CAP money from the signing bonus. Maybe a deal can be put together that works, but since most players want that up front signing bonus money I would think it's hard to do. If it were easy I think you'd see it done all the time. Hopefully someone else can explain it better and in more detail.