I would just make tucks between the scallops. They could be hand sewn seams, pretty easy to do, but I would leave it until you are done quilting to within a foot or so of the edge. At that point you would know exactly how much of a tuck to make at each area. Just leave enough of the top unquilted so you can flip to the wrong side to make the seam with a running stitch (easier than sewing the tuck with an invisible stitch from the top).