i think i kinda understand what you're looking for....
if you are using PHP, the easiest way would be set the include_path directive in your php.ini file.
if you are using Perl, set the path where your include file is located into the Perl include array; for example, if your include file is called "include.pl" which is located in "/some/location/", in each Perl script, do this:
push @INC,'/some/location/';
use "include.pl";
Urb's suggestion about using the SSI include will work too
hope that helps a bit... unless i am completely wrong about what you're looking for
