Sign me up for a 3-d printed mod! The bottom of the stick flared out to fully cover the disc and give the maximum gripping surface area. A quick Google search for oversized chess pieces yielded some cool results, especially the glass ones which look amazing. The room idea is great since there would be a concave surface to cup the thumb! What's the worst thing that could happen?
Smart money would be to find someone who has one and loves 3D printing and a challenge! Send them a Flashback controller to use and abuse in order to create a working disc replacement.
Once this guy/gal got the joystick correct get them to make 10-30 sticks.
Its more than just owning a printer but also knowing how to use 3D design software in a way that you could design a stick that works.
At the moment i am going with a Bishop Glued to a Flashback controller because i know no one with a 3d printer.