Thanks for posting that link pinecone. That's gonna come in handy. I wish I'd known about that technique awhile back when I was just a little short on a particular fabric and didn't want to make a pieced backing. I'll be using this idea at some point I'm sure.
Piecing the backing can solve the problem of having fabric that is just shy of your width too, if you're up to doing a little more piecing. Just bring some of the fabrics that you've used on your top around to the back to make an interesting back. I've seen some really wonderful pieced backs. I've made one that I really liked. Usually by the time I'm done with the top, I don't want to make another "top" for the back, but it can be a great back "widener" and make the back more interesting, and you don't have to make it all that complicated. You can also just add a wide enough strip of some of the fabric used on the top if you have any left, or a fabric that would compliment it. I try not to have to buy the double length if I'm only a few inches shy. :)
Gosh, I nearly forgot to mention how absolutely adorable that quilt top is!! It's very sweet.