"Proper" airlines generally aren't very picky about the weight of your luggage, so it probably wouldn't apply to them, only to airlines like Ryanair that are.
I don't think it's a good solution, but I can relate to to bitterness of being charged for a 2 kg overweight and then getting stuck in half a seat because the person next to you is the size of a cow.
Seriously the implications of that are boggling although I suppose modern technology makes it possible to do so.