Thanks for the responses. I decided to just tuck and not use string (they're in the Smokette now). I kept thinking back to those roasts my Mom would make in my "yute", where the butcher would tie up the beef with a string net. I remember the netting getting discolored from the blood/juice of the roast.
I'm still concerned about the ragged end getting overcooked, but it all gets shredded for delicious pork BBQ sammijes so it's all good.