After thinking about it for a while, doing some maths, and doing some checks, I think I have a method to manually machine an arc on a mil without using a rotary table. I would appreciate it if someone would look to see if I missed something or not:
http://benchtopmachineshop.blogspot.com/2013/05/arc-interpolation-on-manual-mill.html
http://benchtopmachineshop.blogspot.com/2013/05/arc-interpolation-on-manual-mill.html