I'am trying to add a listener to the Gmap extension, so my users can add a marker on a
map with a click.

With standard javascript and google map api i would added this code to the Gmap2

GEvent.addListener(map, 'click', function(overlay, point) {
    if (point) {
        map.removeOverlay();
        pin = new GMarker(point);
        map.addOverlay(pin);

        document.form.gps_lat.value = point.y;
        document.form.gps_lng.value = point.x;
    }
});
But i can't figure out where to add this to the Gmap Extension

Thanks for your help...