How do you do this? My Pioneer 1140 has better stretch modes as well but even thought the HR20 is outputting 480i it forces you to select a "format" because you setup a 16:9 TV in the options. It never sends an unaltered 480i SD signal to the TV! If you cycle throught the 3 formats (I have native=on), pillar box actually adds piller boxes to the SD and formats it for 16:9 so when the TV trys to stretch it, the HR20 pillar boxes are considered part of the frame.
Sorry if that doesn't make much sense, but I just got my new TV hooked up this weekend and have been frustrated by the lack to pass a completely unaltered signal to the TV. Maybe I am missing something...