I think it was Burchquilts that posted a link this week of a nice little quilt with a super cool back. The picture was of a back with 2 different colours joined in the center with a giant zipper effect? You could do the same with your back and maybe add white for the zipper effect to tie the front and back together. Maybe Burchquilts will see this reply and repost the link? I know that I am going to use the design on a quilt back myself.