My cabinet is a modified Bad Dudes as well so I feel your pain. I wanted a swappable control panel system so I could have a true Tron panel as well as a few 2-player panels that feature different joysticks. I had a little dilemma because I wanted to fit a lot on the main panel to avoid having to swap the panel out all the time. I wanted a 2-payer/seven-button layout plus a trackball and a dedicated 4-way leaf switch stick. You already know that is an impossible task for the tiny control area on the Bad Dudes cabinet.
To solve this, I knew that I would need to build a larger control surface. Eventually, I found someone who works in an auto body shop to build me some custom metal panels. The basic design keeps the width and slope of the original panel but extends it a good six inches. It's sort of parabolic in design and extends a little bit down the front of the cab. There is enough room above the coin box to do it. To keep the panel in place, the top slides into a slot and the bottom clamps directly onto the cabinet. Haven't had any troubles with it coming off.
I can't send you pics because I'm digital camera-less right now. If I can borrow one, I'll send you some. Good luck!