I just saw one beautifully done. The repair quilter measured the for the widest part of what she would need to add to the DWR quilt edge. She cut the new border fabric and starched it. Then she basted the edge of the old quilt around the scallops and removed the binding, put the new border on top of that, pinned it RST, and sewed around the scallops with the scallops facing up on her machine. It looked great. She finished with trimming the new border at the old scallops and bound with bias fabric binding.
It was really neat.