Almost any pattern can be done that way. So long as you don't stitch all the fabric to form a square or rectangle, then you have enough unstitched fabric to put a circular or oval frame around it or you could use a mat that's circular or oval with a square or rectangular frame.
You could use backstitches to "frame" the area that is to be stitched to be sure you fit within the area. It's not a true circle or oval but it should give you a general idea.