It's really not difficult to do a border like that. The difference is that I don't measure the body of the quilt through the middle but on the sides. That can cause it's own problems but fortunately, the sides of the quilt were exactly 60 1/2" as they were supposed to be. I measured out 30 1/4" from each side of the center of the border motif, which I chose to be an inward facing point of the scallop after roughly laying it out to see that the outward circles would be at the ends. I mark the two ends of the borders and line that up with the edges of the quilt. I could have gone from the center of the outward curve and had the corners meet at an inward facing point too.
On the next border that meets one already sewn on, I measure out 30" from the center to subtract the 1/4" taken up by the opposing border.
If it wasn't a square quilt I don't think it would work with most fabric repeats. As long as the center point of the quilt is lined up with the same point in the border repeat on all sides, it should line up at the corners.