This is no way presented as a tutorial - simply an idea/concept being explained, should you attempt these modifications do so at your own risk!
- Get Buzz controller from your Wife, Girlfriend or local charity shop
- Unscrew Buzz handset completely
- Find the ground for the lower board & solder your ground (use 7 cable/wire for all 5 buttons)
- Solder the 4 lower buttons to your wires (easiest at the actual tact switches)
- Find the ground for the upper board & solder your 2nd (separate) ground
- Solder the fire/buzz button to your cable
- Feed cable through Buzz handset casing (I snapped off the screw point)
- Feed opposite end through Atari/joystick casing
- Slice circuit board to allow the fire button its own ground that was taken from the upper board
- Solder remaining wires & ground to their points
- Close up & rinse n' repeat
Watch the video, if this all seems vague, these are just notes after all. To be fair if your even reading this you probably have the skill to attempt it - so just consider this piece a concept and utilize however you see fit.
I did use the programs JoyToKey and Vjoy to map the buttons to either key presses or virtual joysticks.
Making Vice make use all 4 was tricky, as I had to set half the pads to key presses and the other 2 as virtual joysticks. I can confirm this works (as shown) in the Vice emulator.
The game featured is the incredible Bomberland, available as a digital file or an actual cartridge from RGCD.
I imagine people using/building MAME cabinettes could get use out of this method as you could use to wire up 20 switches.
Enjoy, and if you need further info - DON'T DO IT!