I'm doing a Montana Cartwheel which is very similar to the NYB. I was taught to use freezer paper. I do not stitch through the paper, but fold it back, trim and then stitch on the next piece. Then I iron it down and start the process again until I get to the end of the arc. When the arc is covered with fabric triangles, you just trim off the fabric pieces hanging over the edge of the paper.
I'm really enjoying it and it looks so neat an precise when done. :D