As you say it is bad design. Why not just call a user method on the object - this method just needs to know where to go for its data? But as (almost) always Perl will accomodate you.

package Bad::Design;
use Data::Dumper;
my $o = Bad::Design->new();
print Dumper $o;
print $o->parameters->user, $/;
$o->parameters->user('Matt Wright');
print $o->parameters->user, $/;

sub new { bless { 'params' => { user => 'Randal Schwartz' } }, shift }

sub parameters { bless $_[0]->{'params'}, ref($_[0]) }

sub user{ $_[0]->{'user'} = $_[1] if defined $_[1]; $_[0]->{'user'} }

__DATA__
$VAR1 = bless( {
                 'params' => {
                               'user' => 'Randal Schwartz'
                             }
               }, 'Bad::Design' );
Randal Schwartz
Matt Wright
[download]