Edit in JSFiddle

Event.definePseudo('right', function(split, fn, args){
    var event = args[0];
    if (event.rightClick) fn.apply(this, args);
});

document.id('clickme').addEvent('mousedown:right', function(){
    this.highlight();
});

<div id="clickme">You can click me with the right mousebutton</div>

#clickme {
    display: block;
    padding: 20px;
    font-size: 2em;
}