That's how I do my cornerstones and sashing. I also strip piece them. That is, if my blocks are 12-1/2" and my sashing and cornerstones at 4-1/2", then I'll cut a strip of the sashing fabric 12-1/2" x WOF. I also cut a strip of the cornerstone material 4-1/2" x WOF. Sew those two strips together into a strip set and then subcut into 4-1/2" strips. The beauty of this is that the sashing strips are cut lengthwise of the grain and, once you sew them onto the block, your sashing strips have almost no stretch and all your blocks fit together so much easier.