You could complete a current loop from your switch and employ an optical isolator at the receiving end. This will work with very long cables and it will tolerate common mode voltages that would cause errors in or even destroy non-isolated transmission circuits.
If you need sharp, well defined signal edges at the receiving end then you can use a schmitt trigger at the opto-isolator's output to clean up the signal before passing it to the receiver logic circuitry.
So, apply a dc voltage across the series combination of opto-isolator, resistor and your remote switch. The switch sits all by itself as far away as you like from the other components, out at the end of a long cable.