I made animated pivot solution last year, but I had forgotten most of it. So I wrote notes for my own understanding and to share with others. Here are the links.
Part 1 (http://leftbulb.blogspot.com/2011/04/making-animatable-pivot-part-1.html)
Part 2 (http://leftbulb.blogspot.com/2011/04/making-animatable-pivot-part-2.html)
Hopefully this can be helpful to someone. If there are any suggestions to improve it, please let me know :)