Inspired by a thread on the iRacing forums, I decided to try building my own button box. For only $20 worth of parts, you can't go wrong. :D
First I made a template of where to drill for the buttons.
Then I marked them with a center punch.
Then came drilling them out.
Installed the buttons.
Then the wires and encoder.
Finally, put the two halves together and put on the end plates.