If the ball strikes the striker's person, any runs scored are credited as leg bye extras provided that the striker was either attempting a shot or trying to avoid getting hurt.
For balls whose trajectory would clearly miss the stumps (hence, LBW doesn't apply), the batsman can line up his bat alongside his leg, and then kick the ball while moving the bat in sync with the leg. This makes it appear he was attempting a bat-pad shot, making him "eligible" to score leg byes while eliminating any possibility of getting out caught. There could be other "creative" ways of faking a shot while deliberately hitting it with the leg, as well.
Is this kind of misuse allowed, and if not, what is the provision in the laws against it?