It can't - it is hardwired into the Garmin CCU, not NMEA 2000. It is a flow switch which closes when the wheel is manually turned; it will close when fluid flow is in either direction. Depending upon the sensitivity setting is how the Garmin AP reacts. If on a heading hold and the system reacts to manual input it will temporarily allow control from the wheel then after a period of time (short) will resume the heading hold whichever way the boat is pointed. If following a course and the wheel it turned it will disengage the course and the AP will need to be re-engaged. Here is how it's wired -I'm wondering if the Shadow drive valve could not be added to any AP install?
Even if it just drops the head unit into standby mode, that would be a befefit, but could also be a pain depending on how sensitive it is...ie if I bump the wheel, would it drop out.