Dialog Position - don't extend below viewport

Dialog Position - don't extend below viewport

I want to open a dialog so that the top of the dialog is just below where the person clicked their mouse - so the click event has this:
  1. $('#dialog').dialog({
          autoOpen:false,
          modal:true,
          width:740,
          closeOnEscape:true,
          resizable:false
    });






  2. $('foo').click(function(event)
  3. {
  4.   $('#dialog').dialog('option','position',[(event.clientX - 90), (event.clientY + 30)]);
  5.   $('#dialog').dialog('open');
  6. });
In my case, the dialog is larger than the viewport - and I *do* want it to extend below the viewport (causing the browser scrollbar to appear).  Regardless of what I set the postion to be, the dialog appears above the viewport so that I can't even drag the title bar - and no browser scrollbar appears for me to get up to the dialog.  I've seen people report similar issues and there's something with regard to the collision detection.
Is there an option I can set when I initialize the dialog to prevent it from happening?