Ya can make a lot of ideas, but the fact is that how it is made right now, makes it almost impossible.
If you have a female avi, check max-min size, and check the difference with enabled or disabled physics.
Think of it like a jelly stuff added to the breasts zone. if you spin your avi in the editor, run, or do stuff, that affects the boobs making em bounce, have some centrifugation effect and so. even if you make em the smallest possible that still affects that zone. No other zones are affected like that. All the others are premade stuff, with standard sizes, no changes, nothing else.
If you run, the penis doesnt swings like a crazy sausage flapping everywhere like crazy stone eyes, like boobs do, it moves the way it was mean by the ones that made that animation.