Multisite and dynamic configuration items in Drupal : help from Apache

Having recently merged a number of separately configured sites into a single consolidated multisite, I found myself with URLs like:

...on all except the main site of the multisite configuration.

Although img_relocator allows me to just type things like:

<img src="somefile.png" />

... and still have these URLs be automagically generated, they still appear to those users who actually look at the URLs.

Enter mod_rewrite

Abandon all hope, ye who enter here

With these sites running over Apache 2.x, mod_rewrite offers a simple way to rewrite the files URLs: in the Apache site definition file for the vhost describing the site, we can use: