As already somehow suggested in the comments, I think the most easy thing is to get a solution to your “I don’t want to duplicate template files all over the place because they contain all the same” by modularizing those.
E.g. by using template parts – and I think that’s even more powerful – by hooking into the template loader (see template-loader.php). See as well Template Actions (WordPress Codex)
and the WordPress 3.0 Program Flow (Toolpress PDF).