Decent idea, though there'd need to be a system in place to make sure it's not abused, similar to the forfeit button's requirements.
I personally believe a stalemate button should not divide the eliminated players points up; by definition, a stalemate has no winners, and should people decide they don't want to finish a game, they shouldn't be rewarded points. It is also, in my opinion, a very easy to abuse system if that's the case; join 3-8 player game with your friend, play until you're the only two left, stalemate and divide the points of the losers.
Rather than create a system that people can abuse, simply make a stalemate just that.
That being said, you can always add round limits to your games as well; nothing's stopping you from throwing that 100 tag on there.