Originally Posted by MacG
There is a tool (I saw one one time) that consists of two metal blocks that are clamped in a bench vice. Each block has two hardened pins protruding that are designed to grab two teeth on each side of the cog. You set the width to match the cog in question, clamp then securely in a bench vice, and then use the wheel for leverage.
That's the one I was trying to draw. Freewheel has one.