Try calling: Code: pcmanfm -w <image file> I don't know if it works but that's what's written in the manpage. If it works, add that command to the orientation script.
pcmanfm -w <image file>
That tapping outside thing sounds ingenious if it works as you described (not sure if the screens of all the N900s are equally responding). That would actually allow to have four panels, one on each screen edge.