Multiple MW installations on one Apache

I have multiple MW installations on a single Apache Webserver. The steps given here mention the short URLs considering that there is only one MW installation per Webserver.

Anyone got an idea as to what to do do to make multiple clean URLs on multiple installations but on same Webserver.

eg: http://<generic URL>/<specific installation 1>/Page_name_X http://<generic URL>/<specific installation 2>/Page_name_Y

For security and company policy reasons cannot share the exact installations or paths as it is not live yet on Internet.