Can I fix my broken command dial myself?

I had exactly this problem. Used s9500s are not particularly expensive and after the command wheel came away I more-or-less wrote it off. But before finally doing so I decided to see if I could fix it myself. By that time, the plastic flanged collar had gone missing, but, amazingly, the control knob was still lying around. You can follow in my footsteps and avoid some of the mistakes I made.