Well, you can skip Exporter.pm and constant.pm, since doing it yourself gives you more flexibility. For example:

use strict;
BEGIN {
    my %consts= (
        CA => 1,
        AZ => 2,
        UT => 3,
    );
    while(  my( $name, $value )= each %consts  ) {
        no strict 'refs';
        *{$_."::".$name}= sub () { $value }
            for  qw( A B C D );
    }
}
package A;
print CA,$/;
package B;
print AZ,$/;
package C;
print UT,$/;
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But whether that is an improvement depends on a lot things, including taste.

        - tye (but my friends call me "Tye")