What about sewing with invisible thread and basting up on the top by the binding where it won't show the sewing line and then hand stitching it on the bottom of the sleeve, so as not to catch or interfer with the front quilting. All of the weight will be on the top of the sleeve and should hold it temporarily. As soon as the show is over you can just pull the plastic thread out and unstitch your hand casted thread on the bottom.