Some other options:

1. Mixin/Role/Trait. Gives every object that needs it a config method.
2. Config factory. This is a singleton itself, but it can hand out configuration objects to whoever requests it.

The mixin is conceptually very simple:

package My::ConfigMixin;

use base qw/ Exporter /;
our @EXPORT = qw/ config /;

sub config {
    my $self = shift;
    somehow_get_config(@_);
}
[download]

Which, when used (a simple use My::ConfigMixin; will do), gives your object the method config. Since its first param is your requesting object, you can do all sorts of filtering based on $self (access control, limiting output, etc).

The main issue here is maintaining state. Pretty much your only option is to use package variables in My::ConfigMixin, which can get messy. I'd be interested to learn more about Traits that need state, but sofar I'm a newbie on the subject.

The factory might be a better alternative: it can maintain state on its singleton instance.