There's some rather scary LaTeX hackery involving putting a picture environment under every page and using \includegraphics to put an image into that environment. You'll have to adjust the size of the image using the width option, and if you want even and odd pages you'll have to check the page number to know whether to shift the image right or left by changing \put(0,0) to \put(3,0) for example.
For page number testing try something on the order of
\ifodd\count0 ...stuff for odd-numbered pages ...
\else ... stuff for even-numbered pages ...
\fi
This isn't really a full answer but will be enough to get you started.