Since I love pieced backings, I incorporate them into the backing. I like it when it is a computer printed message, poem, or saying pertinent to the quilt and my mood or who the recipient is.
I would maybe make some sashing so they are closer to the same size then leave an empty space for a plainer fabric with the saying [or whatever] on it. You can do the horizontally [which I prefer] or even diagonally or vertically as you desire.
It is fun and helps get me out of my 'box.'
ali