Why heat/cool the whole car?

At this age of skyrocketting energy costs why can't we just heat the front portion of the car alone? A whole majority of the cars on road carry just a single person (the driver) or utmost one additional passenger. So can't we have a movable separation (like the ones in some cabs or the cover of a convertible) that slides behind the two front seats? At the push of a button we can close this "door". This way we just need to cool/heat only the portion where the occupants are present. No need to waste energy heating the back row of seats and avoid heat loss due to leakage associated with a larger area.