Well, PYGGEL does support sky boxes, allowing you to put a box or
sphere around the entire scene.
You could write a simple SkyBanner class that just ignores the camera
to put an image there.
Or you could load the image as an Image2D and use the view.set2d/
set_lighting(False) commands (you'd have to switch back for the rest
of teh scene though...)
Or just build two scenes, the first only having the background, the
second everything else.
Render the background first and then proceed as normal.