Serving multiple directories outside of web root from the same URL with Apache2

I've got this working through mod_rewrite. I updated the vhost configuration directly instead of using an .htaccess file. I believe it could work through the .htaccess but my rewrite rules were a bit off (note the missing /). It was also necessary to add the <Directory> declaration (to allow access) for the image directories.

The vhost looks as follows:

DocumentRoot /var/www/html
<Directory /var/www/html>
  Order allow,deny
  Allow from all
</Directory>

RewriteEngine on

RewriteCond "/mnt/imagestore1%{REQUEST_URI}" -f [OR]
RewriteCond "/mnt/imagestore1%{REQUEST_URI}" -d
RewriteRule ^/?(.*)$ /mnt/imagestore1/$1 [L]

RewriteCond "/mnt/imagestore2%{REQUEST_URI}" -f [OR]
RewriteCond "/mnt/imagestore2%{REQUEST_URI}" -d
RewriteRule ^/?(.*)$ /mnt/imagestore1/$1 [L]

<Directory /mnt/imagestore1>
  Order allow,deny
  Allow from all
</Directory>

<Directory /mnt/imagestore2>
  Order allow,deny
  Allow from all
</Directory>