Hey Reg, set the sprockets up on a rotary table, make a plunge cut with a hollow end mill, the nub left can be the faux bolt. see link,
http://ecx.images-amazon.com/images/...JL._SX342_.jpg Then index to the next bolt position, new plunge cut with depth stop. Clean the rest up on the lathe later. Hope this makes sense?
Cheers, Neil.