You could probably use some kind of perfboard to hold the buttons in the right shape, and then just screw said board to the shell. As for securing the buttons to the board, just use a tiny dab of superglue or hot glue.
You could probably use some kind of perfboard to hold the buttons in the right shape, and then just screw said board to the shell. As for securing the buttons to the board, just use a tiny dab of superglue or hot glue.