serve items in "lib" or "PATH" fashion

Hi.

I run a series of mostly-identical websites under Apache2/mod_perl2 (and Template::Toolkit).
Most of the time, these websites use a common /js/*.js javascript snippets directory, a 
common /cgi-bin/*.pl directory and so on. This is done via Alias'es in each website's 
<VirtualHost> configuration file, pointing to a common location.

However, once in a while - tending over time to become "quite often" - one of these 
websites will need a modified version of for example one of these javascript snippets or 
cgi-bin scripts.  At the moment, I solve that by giving this website, then, its own 
/cgi-bin/ directory, copying *all* the standard cgi-bin scripts there, changing the 
/cgi-bin/ Alias to point to this own cgi-bin directory, and then modifying the one cgi-bin 
script that is special for that website.

But of course then I am stuck forever now with this separate cgi-bin directory to 
maintain, containing not only the one script which is different, but all the others too.

I would much prefer if I could give each of these <VirtualHost> sections a list of 
directories in which to look for a target document or script, much like the way in which 
the PATH or PERL5LIB variables are used.

E.g. I would be happy if I could write this in the Apache configuration :

ScriptAlias /cgi-bin/ /var/www/site1/cgi-bin/;/var/www/global/cgi-bin/

and have Apache look first in the local one, then in the global one each time it is 
looking for a given script.  And similarly for other documents like javascript libraries.

Now my question is : does anyone know of an Apache add-on module doing something similar ? 
; does anyone know of an add-on mod_perl module which would do something of the kind ?

I have already searched, but as I do not know exactly which terms to use for such a 
search, I have not found anything yet.
I'll write my own PerlFixupHandler or so to do this if I have to, but if it already 
exists, I would not bother.