When hollow grinding, it used to bug me that I couldn't change direction between grits, like I do when hand sanding flats. One day, it ocurred to me I could just leave the grinder turned off and 'hand sand' from point to tip by pushing the blade back and forth across the wheel. I really don't know if this has any application for what you are trying to do, but if you could find something with appropriate radius - even a cheap bech grinder, you might be able to work something out with coarse (and then finer) wet/dry paper.
Rob!