HDR's flashcart for the gameboy camera has a switch to switch between 2 different roms, This extends the switch to a gap you cut in the original shell.

To cut the shell lay the switch extender onto the switch in the up position mark on the shell then put it in the down position and mark the shell. Next cut down on the 2 marks then snap it off with a pair of pliers.

HDR's gameboy flashcart - https://github.com/HDR/Gameboy-Camera-Flashcart

The switch was remixed from this - https://github.com/hatchman/Game-Boy-Camera-Shell