I started by using the answers here, but modified it to use YouTube's new iframe embedding...
$('a.more').on('click', function(event) {
event.preventDefault();
$.fancybox({
'type' : 'iframe',
// hide the related video suggestions and autoplay the video
'href' : this.href.replace(new RegExp('watch\\?v=', 'i'), 'embed/') + '?rel=0&autoplay=1',
'overlayShow' : true,
'centerOnScroll' : true,
'speedIn' : 100,
'speedOut' : 50,
'width' : 640,
'height' : 480
});
});