For regular Chinese buttons, see ShinSanwaSwitch by @steelpuxnastik (LHSXF "clone" for Chinese buttons). For hori buttons, just remove the keyboard switch and epoxy a piece of cardboard on the actuator, then epoxy the photointerrupter near the switch holder so the cardboard can pass through the opening gap of the photointerrupter. If you want more precision, you can probably make a T shaped piece in OpenSCAD or something, 3D print it and epoxy it to the actuator. Use any weaker glue (e.g. double sided tape or hot glue at low temperature) if you don't plan to make the mod permanent and willing to sacrifice some vibration resistance.