I do something similar but before using the hole saw, I often cut 3, 4 or even more smaller holes, depending upon the size and shape desired, around the perimeter to create notched knobs. Handy when you need a little more grip. 3 larger holes will give you sort of a 3 wing knob and 5 or more small holes give you one sort of with detentes around the perimeter.
--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.