Ok, a few weeks ago I added a hanging sleeve on a quilt and thought I'd show you how I did it. Someone probably has a better way- if so, I'd love to see it!
I ironed it wrong sides together and lined up the raw edges (of the quilt and sleeve) and pinned heavily so it wouldn't move around. Then I added my binding to the front as usual, making sure to catch in the sleeve on the raw edge.
Unplanned, but you can hardly tell there is a sleeve.