Seeking Wordpress-Apache conf that allows for dynamic subdir-to-site creation

Question

Seeking Wordpress-Apache conf that allows for dynamic subdir-to-site creation. Specifically, want to create any of these /var/www subdirs on the fly:

/var/www/main
/var/www/siterev1
/var/www/siterev2

and place a WordPress install in each one (easily done with git branches), and have above installs/dirs/sites map, respectively, to the following:

http://my.com/main
http://my.com/siterev1
http://my.com/siterev2

...all without any changes to Apache conf as subdirs are added. (eg: adding /var/www/siterev3 would enable http://my.com/siterev3 without any Apache conf changes.) This is a rather std config for Apache-to-dir path mapping, but can't get it to work, and am guessing the Apache mod_rewrite config (in Apache config below, comes form "std" WordPress install instructions) is not flexible enough.

Answers like this hard-code the site/path/subdir name in the Apache conf. Want to avoid this. Alternatively, if we must hard-code Apache conf, we'll go there (begrudgingly), but don't even know how to do that.

Current Apache config follows (running on Ubuntu 11.04 or above). Have tried a few tweaks gleaned from other posts/answers, but nothing's yet worked (and most configs appear to hard-code the subdir/site references).

DocumentRoot /var/www
<Directory />
    Options FollowSymLinks
    AllowOverride None
    <IfModule mod_rewrite.c>
        RewriteEngine On
        RewriteBase /
        RewriteRule ^index\.php$ - [L]
        RewriteCond %{REQUEST_FILENAME} !-f
        RewriteCond %{REQUEST_FILENAME} !-d
        RewriteRule . /index.php [L]
    </IfModule>
</Directory>
<Directory /var/www/>
    Options Indexes FollowSymLinks MultiViews
    AllowOverride None
    Order allow,deny
    allow from all
</Directory>

Answer 1

I would try something like this. It may need a bit of tweaking as I'm used to putting mod_rewrite config in the server/VirtualHost context, not in a <Directory> block, but the idea should hopefully be clear enough.

<Directory /var/www/>
    Options Indexes FollowSymLinks MultiViews
    AllowOverride None
    Order allow,deny
    allow from all
    # Put all the mod_rewrite rules in the Directory where the actual
    # web content is found, not in <Directory />
    <IfModule mod_rewrite.c>
        RewriteEngine On
        RewriteBase /
        # Let through any access to index.php - can tweak this to only
        RewriteRule ^.*/index\.php$ - [L]

        # Grab the first component of the requested path, then use that in the
        # RewriteRule substitution. So e.g. fish/saltwater/shark.php ends up
        # internally redirected to fish/index.php, and animals/cats/tiger.php
        # is rewritten to animals/index.php - without naming either of the
        # directories in the rule.
        #
        # N.b. the regular expression in the RewriteRule roughly means "all the
        # characters before the first forward slash in the request path", which
        # should grab the subdirectory name.
        #
        RewriteCond %{REQUEST_FILENAME} !-f
        RewriteCond %{REQUEST_FILENAME} !-d
        RewriteRule ^([^\/]+)/.*$ $1/index.php [L]
    </IfModule>
</Directory>