I can imagine compromise in form of a thread where people who play from the same network will announce they will do so and state name of their characters they will play with, so admins can make random controls of logs where they can see if they really behave like two (or more) players or it´s one player running more than one character, for example on his PC and laptop. Usually it becomes obvious sooner or later. Not registering in this thread while doing trading/mining will be still considered as a rule violation.
