I have used this a couple of times, and it works great when the backing is just a bit too small. It saves quite a bit of yardage. When the backing is 1/3 of it's width narrower it is just about even. Use the calculator (you'll have to download the worksheet for it to work for you). I've shared to see if it is worth it for you. If you save fabric and it's worth the time, here is the method. Make sure you remember to add to the width and length in your quilt measurements so it is larger than the quilt. Add 4-6" and use those measurements in the calculator.
(You can click all pictures to make them larger)
Here is the backing ready to be pinned to the top. Since it's fleece, the seam is very obvious. It can't be pressed, so I just make sure it's open when I put the top on and pin.