Just attach any off the shelf step engine to the potentiometer you have now. Turn it all the way to zero and count how many steps you have to the maximux value. Then it is just to make sure you never step outside these min and max values.

To be safe, don't screw the potentiometer straight on the engine axis, instead align the axis parallell to the Knob and put som rubberbands as a driving belt. That should give you room for minor misstakes in the software development :-)

Not the neatest solution but definatly the fastest one.

And you can always just remove the stuff and you are back to where you are now.... Hey hey hey - a true Krusty the clown design!!!