You can hand sew a sleeve to the back, just take care not to stitch into the front of the quilt. For a temporary sleeve you could just use muslin. The top of the sleeve could be right under the binding as near as you can get, but so you can easily stitch. For a temporary sleeve, you wouldn't have to worry so much about the stitching being really close together. Just make sure that both sides are really secure at the ends.