I have seen this behavior both controlled by an extra mechanical pin in the audio jack and also by a feature on the audio chip which was ultimately controlled i

I have seen this behavior both controlled by an extra mechanical pin in the audio jack and also by a feature on the audio chip which was ultimately controlled in software. So it's hard to tell whether that would work. Also consider that if you played the sound at maximum volume it might actually be audible some distance away from the headphones.