So what would need to happen is that SiteConfig would have to export a "$c" that is appropriate for the current request (based on some way to determine which of four domains it's serving). That doesn't even seem possible (to export something different at run-time when it's loaded when mod_perl starts).

Tied variables allow you to have things that appear to be variables but are in fact subroutines.

package SiteConfig;

use strict;

use base 'Exporter';

tie our $c, 'SiteConfig';

our @EXPORT_OK = qw($c);

sub FETCH {{
  dbname => 'somedb',
  dbserver => 'somehost',
  dbuser => 'someuser',
  dbpass => 'somepass',
  site_name => 'Some Plain Text Name',
  domain => 'some-domain.com',
  #... and a bunch more ...
}}
[download]