I would not unstitch the binding to add the sleeve because a good pleated sleeve needs to be sewn somewhat below the binding in order not to be seen above the quilt when it is hanging. This is especially true because you do not know the size of the rod the owner will be using. Here are some simple instructions for making hanging sleeves.
http://quilting.about.com/od/decorat...ilt_sleeve.htm I make mine 2" inside each side edge and an inch below the top edge and always make them from a 9" wide (cut) strip.