You have to catch the event and trigger the SAME event on the 'underneath' element.
I made a fiddle (http://jsfiddle.net/Q5HtP/) for you, keypart:
var stage = document.getElementById('stage');
var pano = document.getElementById('pano');
pano.onclick = function(e) {
var event = new MouseEvent('click', e);
stage.dispatchEvent(event);
};
stage.onclick = function(e) {
console.log(e);
alert('click');
};