Forgive me if what I say is stupid, but I'm only a GA SEP pilot so a "pushback" is something I've only ever come across on those treasured jump-seat rides.
If the tug pushing on the nose-wheel while the brakes are applied is such a great risk to the aircraft (and the statistics seem to suggest that it is), why is there not a clear set of "traffic lights" in the nose-wheel well visible to the tug driver and/or ground engineer? These should be linked to the braking system such that brakes applied == red light, brakes released == green light? The system could also be linked to any other critical systems, for example thrust-levers above ground-idle == red light, or even beacon off == red light.
Just a thought...
MD.