Hi Jesper,
This is probably not an area where mod_rewrite should be applied. Use
Alias instead in each of yuor vhosts. If repetition becomes an issue,
consider using mod_macro.

Reply if you need specific help with Alias,
noodl

http://httpd.apache.org/docs/2.0/mod...ias.html#alias
http://www.cri.ensmp.fr/~coelho/mod_macro/