Mod_rewrite And Archiving Directories -- SE Issues

I have many directories from years ago on a fileserver. Many of them are indexed on Google. I have five webservers reading from one fileserver for the data. I'd like to keep copies of the most recent data on the webservers and through mod_rewrite tell it to use local copies instead of reading through the fileserver. I would like to move most of my older directories into an "archived" directory.

If I move most of my older directories into an archived directory, the Google listings will then 404. I could put a 404 doc up redirecting to the index page, but Google will drop the link, which I would like to avoid.

I could add a new RewriteCond / RewriteRule (below) for each new directory. But, it would need to be added in the httpd.conf file for each of the webservers and restarted. With the number of new directories I add, this would be infeasible.

Does anyone know of a way to accomplish what I am trying to do? I do not need the older directories in the "archived" directory to be accessible or rewritten, I just don't want to lose the search engine listings from them. And, I want to reduce the strain on the fileserver for these files.

I also don't know of a way to say: rewrite everything locally unless it is in the /dir1/archived directory and if there is a 404, the directory probably existed at some point, redirect that to the index and give a 200 status code.

Does anyone have any suggestions? I tried mod_cache but it doesn't seem all that speedy.

RewriteEngine on
RewriteCond %{REQUEST_URI} ^/dir1/dir2
RewriteRule ^/dir1/dir2/(.*)$ /path/to/dir1-localcache/dir2/$1