Restrict Dragging with Sortable Portlets

Using the example of the Sortable Portlets:
http://jqueryui.com/demos/sortable/#portlets
Is there a way to modify it so that the portals are only dragged when
you click on the "portlet-header" divs, rather than the containing
"portlet" div
Basically, I want the Portlet to move if you click on the header bar,
but not if you click on the content.
Thanks,
Andy