Well, I thought I would give this a try but it did not turn out too well. It worked a little but I think I would have had better luck if I had cut my binding on a bias instead of on straight of grain. Then it would have had more stretch.
Here is the link to the tutorial, which was very good and I loved how it came out.
Cathedral Window rolled type binding
Just wanted to give my suggestion to try a bias binding if you want to try this. I made my scallops approx. 4.5-4.75 apart and still the middle did not want to give enough so my scallops are not so deep. Also had to add a pic of my helper???? He approved if I would just pet him once in a while.