I haven't seen this thread before, so I thought I would mention my set up in case it helps anyone.
I set mine up using a microswitch that had a lever arm (from an old broken joystick). I attached behind the reject button so that it would activate with a light button push but could accept even an extremely hard push by allowing the lever to bend. I initially put the switch on the lower arm to deactivate on pressing the button, but I found that the arm didn't always return all the way and thus didn't close the standard microswitch. This way eliminates the only real problem with locating the switch directly behind the reject button IMO.