looks to me like if your pinwheel is say a 5" finished block, then you would need a 2 piece strip block that finished at 5" next to it and also below the pinwheel, and a 5" block next to that strip block. This makes the section a 4 block section.
Clear as mud right?? Maybe someone with a visual can help you. I can't draw it on my computer but I can see it in my minds eye.