Javascript :: How To Call Fancybox Out Of Flash

I want to use fancybox from inside flash. I call a javascript function with

var url:URLRequest = new URLRequest("javascript:callPopup()");
navigateToURL(url, "_self");

and

function callPopup(){ alert("works");}

which works fine. now I want to use this function to open my fancybox content.

the flash content is placed with swfobject. under the flashcontent-div I have my link to the fancybox-content:

<div id="micrositepopup">
<a id="popup" href="images/microsite/microsite.jpg">test</a>
</div>

and I call on pageload

$(document).ready(function() {$("a#popup").fancybox();});

when I click on the test-link all works fine. but how could I call the function

function callPopup(){ $("a#popup").fancybox(); } // not working

to open the fabcybox with the linked content?