I’ve always wondered if something like this would work:

Take a relatively short bit of wire, make a flat spiral at one end about the size of the button, tape that spiral to the button. Then take the other end of the wire hook it up to a relay with the other end attached to ground (or any big metal object probably). I would imagine then closing the relay is “touching” and opening the relay is “not touching”.

I have no idea if that would actually work, but it seems to me like it should. You just need something to interrupt the electric field above the “button”.