Create a marker element, I called mine .footer-marker, placed just above the .footer. Then, use this in the footer's limit function.
limit: function() { return $('.footer-marker').offset().top; }
Here is the modified fiddle:
http://jsfiddle.net/ZczEt/1650/
I removed the summary outer height subtraction as it did not appear to do anything.
Also, the summary now returns a function for its limit as I am assuming the summary has dynamic content. The limit as a function here will compensate for dynamic content loaded into the summary.
Hope that helps.