For users coming back to this post long after the initial answer was accepted, it may pay off to note that now you can use
data-fancybox-href="#"
on any element (since data is an HTML-5 accepted attribute) to have the fancybox work on say an input form if for some reason you can't use the options to initiate for some reason (like say you have multiple elements on the page that use fancybox and they all share a similar class you call fancybox on).