All my pages are generated from a server-side program anyway
(http://www.phpclasses.org/browse/package/1463.html) so I think
I'll look into generating two websites. Each page
will have a "HiRes/LowRes" button the user
can click at any time. Then they can get whatever
suits best.

So I think I've got the solution. Just have to code
it up now.

Thank you all. I think I got what I needed.