Its a good suggesestion, and i think William got it right, but made a little expantion on it. I'd love to see this script be made, it would be awesome. And for those who doesnt understand Williams explanation(no offense): If you hit a joint and it doesnt get dismembered, then you could see if it was close to get dismembered. Example: You hit a Joint and it says 80% damaged. Then it will stay at that damage procent, so if you hit it and give the rest of the 20% in damage, then it would dismember. It could also be expanded by making some joints harder to break than others, and maybe be able to adjust each one of them in singleplayer. I dont know if you understood this better, but its worth a try.
~Ninjabent