I wondered the same thing when I saw it. I wonder if you could make fence/follower to attach to the bottom (a round disk maybe?) that would allow you to follow a curved edge? They sell a straight fence for it but it has a couple of countersunk holes in the base that would allow you to attach a wood base you make. Perhaps you could build the follower into a wood base? Or if you already have their fence accessory, maybe attach a follower to it?
Just thinking out loud.
--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.