Maybe you let people play within a certain distance to each side of the lie center point also. That way certain people, that are always whining about trees, can sneak away from their crappy lies???
No matter how you do it, at some point you are going to have a time and place where players will be getting to the very fine line of fouling, and the call will get tough. The rule simply needs to be something that doesn't give some players an advantage over others. But the more talented players always have an advantage.