I want to set up my webserver so that there are multiple domains names
pointing to the same shared directory on the host server.  The shared
folder should be able to be anywhere in the directory structure.

When one of these domain names attempts to access a file that does not
exist in it's normal directory (httpdocs), I want the Apace web server
to go to the shared directory to find the file.  Very similar to how
the include path works in Unix.

That way, if I need to make a change that is specific for just one
domain, I can just drop a file into the domain's httpdocs folder and
apache will pick up that unique file instead of the file from the
shared directory.

I feel that there should be a way to do this within the apache domain
specific configuration file ... but have been unable to find out how
to do it.

Thank you in advance for working on this.