Introducing the Atari 5200 Keypad Passthru Module.
This device adds keypad functionality to an existing Atari 5200 3rd party joytstick or a previous version of the RetroGameBoyz Atari 5200 Arcade stick that did not have keypad functionality.
Check out the video demonstration:
Cable length is about 4 feet. If you want a longer cable, just ask. I believe maximum cable length can be about 9 feet.