Help with shape class?

Okay so i am using the tween classes and everything works great, loving the results i am getting in contrast to the keyframe tweening, using this article:

http://www.kirupa.com/developer/actionscript/tween.htm

My problem being i want to use the same thing only with shape tweens, can this be done? and if so where is the function located in the flash program files, because I can’t seem to find it.