Magento Best Way to Call Modalbox After Item is Added to Cart

I'm looking for a way to call a Modalbox (http://okonet.ru/projects/modalbox/index.html) after a customer has added an item to a cart...

How do you call a Modalbox from within php? I was thinking of calling the modalbox after the success message in the CartController.php, however, I don't know how to do this from PHP, only from an HTML link with OnClick.