You can do all sorts of curves with a walking foot. I have made flowers, hearts and such with a walking foot. You do have to be careful not to make the curve too tight. There are times that you will have to stop with the needle down and pivot a bit but that's not a big deal for me.
If you go from the center point of each pinwheel you could do a shape like a tear drop/flower petal. Start in the center and you'll end up back in the center at the end so a continuous quilting. You will have to turn your quilt so if it is a large one and your machine has a narrow throat/harp area it might not be possible to do much turning but I don't make king size quilts so never had much of a problem with turning.