i use this method often. there are almost as many ways to add the backing to this as there are to any other top.
you can lay the quilted top onto the batting and tack or tie.
you can add more quilting to hold the two together.
you can also remove 1/4" to 1/2" of the batting around the edges, lay the backing face-down onto the top, stitch all the way around (leaving a gap for turning), then turn it righside out like you would a pillow, and whipstitch the gap closed.
then, either tack, tie, or add more quilting as if you'd done it the traditional way. i really love it when i can use this method because i don't need no stinkin' binding. :P