Based largely on Jason Garr's previous work Sample firmware to interface with the most iPod clickwheels on an Arduino Mega. Should be compatible with most clickwheels as long as you can find the right pinout.
Confirmed working on a 4th gen/Photo iPod using this breakout board. I have a breakout designed for a 5th gen + beyond as well here, however I have not been able to hand solder one properly, and the clickwheel cable itself is a little too thin to be securely mounted.