I took a wall hanging that no longer fit in the room's decor and enlarged it into a lap quilt for Hospice. I saw a video by Sharon Pedersen on THE QUILT SHOW. She sewed the "new back" and the "new front" onto the existing quilt (right sides together back to back, front to front). Then in the existing seam allowance she added the "new batting" by doing a serpentine stitch WITHIN the seam allowance - don't go too wide and go into your new seam. I've done it, it's easy, and it works well. Then, you can quilt your added portion, trim it, and bind. I oversized my added portions so I could trim them evenly afterwards for binding.