Hi!
I'm not sure if anyone has done this yet...
I've experimented on this and it works!:
1) extracted a rotating encoder component from a scroll wheel mouse
2) connected the three legs on the rotating encoder to wires
3) connected the wires to the player - the area where the scroll wheel used to sit on (see attached picture)
4) connected the rod and wheel of the mouse into the hole of the rotating encoder
5) rotated the rod and wheel of the mouse and it scrolls the screen display up or down
Updated:
Picture of my actual player with the connected wires and the mouse encoder.
The wires were not soldered but held down tight by some plastic bits and then glued with epoxy adhesive.
The encoder was attached to a some connector I found from my old pc. It had three holes in it to slot in the mouse encoder component.
It looks messy but it works.