Currently pdflrf generates images that map one to one with the visible pixels in the ereader. The effect you are looking for would mean that the reader would be doing the interpolation and consequently doing a bad job of it. You can test it out by viewing pdflrf's landscape output in portrait mode. Also Sony's landscape mode greys out the bottom and top in landscape mode which is very distracting.
Rasterfarian/PDFRead do what you want in landscape mode. It obviously does not work very well.