I'd turn and stitch the opening as you said, then from the right side pin the three layers together just as in pinning the "sandwich" in the other technique. It can be machine quilted just as the other style. the stitching/quilting pattern might be a little different because, since I"m not squaring up and binding off the edges, I can't just run my stitching off the edges of the quilt. I'd want to make sure that my stitching design would remain on the quilt and come close to the edge to make sure I covered all the surface. Does that make any sense?