package BaseType;

...

BEGIN {
  my $parameter_config = undef;

  # accessor - turns the ParamConfig object into a closure
  sub parameter_config {
    $parameter_config = $_[0] if @_;
    return $parameter_config;
  }
}

sub new {
  my $class = shift;      # the usual prolog
  my $type = ref $class || $class;

  my $self = bless {}, $type;
  return $self;
}

...

##</code><code>##

package Int;
use base qw( BaseType );

use ParamConfig;

BEGIN {
  # create only one of these, at compile time
  my $pkg_name = __PACKAGE__;
  my $parameter_config = parameter_config( new ParamConfig( $pkg_name ) );

  @{$parameter_config}{ 'int_specific', 'params' } = ( 'vale', 'val2' );
}

sub new {
  my $class = shift;      # the usual prolog
  my $type = ref $class || $class;

  my $self = bless SUPER->new(), $type;
  @{$self}{ 'Int', 'Specific', 'Variables' } = ();

  return $self;
}
...

# Thereafter, access the class-specific ParamConfig using the accessor, parameter_config().