Cirque's new sensor that can tell which hand you're using seems like the right (or left?) way to go. If it's the left hand being used on the center dashboard, that's the passenger - unless the driver is doing some crazy contortions, of course. A sensor like this would be useful for the most part, although (like many sensors) probably annoying when it reads things wrong. But still, the more sensors the better, so the whole system can see what's really going on, and work as it's designed.