Using an old volume potentiometer and a Radio Shack knob, I build a turret for my scope.
Caution, with any DIY mod you will have to take your time and there is always a chance of ruining your dust cap.
DO NOT MODIFY A LOADED WEAPON, CLEAR YOUR RIFLE AND REMOVE THE OPTIC.
Step 1: Potentiometer
Use a small screwdriver to bend the tabs and a pair of needle nose pliers to remove the case.
Step 2: Fit the potentiometer to your dustcap
Since the potentiometer does not fit in the cap, a little filing will have to be done. You can use a bench grinder to a faster results, just try to keep the diameter as close to the cap size as possible.
You will have to drill out the cap to fit the potentiometer base. The best technique is a small pilot hole and a step bit. The step bit will help to center the hole if you are not dead on.