When I had my ASUS Transformer Prime, there was a firmware update (ICS v220.127.116.11 I believe) that introduced an unlock settings function related to the system bar, which allowed you to hide/show system information.
You could hide/show the system bar via a swipe of the bar.
This would effectively disable the home/back buttons, which was useful when watching a video, so that you could use the seek-bar without pressing home by accident.
Is this, or something similar, available for the (un-rooted) ASUS Nexus 7 ??