Crazy idea I've always wanted to try: somehow hack a USB foot-pedal to act as a layer key.
(Hard, because usually the layers are implemented inside the keyboard's firmware, rather than being processed by the OS. Maybe the foot-pedal would need to plug into the keyboard.)
(Hard, because usually the layers are implemented inside the keyboard's firmware, rather than being processed by the OS. Maybe the foot-pedal would need to plug into the keyboard.)