Manual:CommonSettings.php

Some Wiki farms use a CommonSettings.php file to contain settings that are common to all Wikis managed by that farm. Since config files are arbitrary php files, you can split up your config files into as many separate config files as you want, and potentially reuse portions among multiple wikis. The Wikimedia Foundation uses a file called CommonSettings.php for settings that are common to all of its wikis.

Possible setup
$wgConf may prove to be useful on such a configuration file.
 * 1) Create a CommonSettings.php file with all relevant common settings.
 * 2) In all of the affected wikis' LocalSettings.php's, add:

External link

 * Wikimedia's CommonSettings.php