use Tie::Autotie 'Tie::IxHash';
tie %hash_ref, 'Tie::IxHash';  # yuck, that variable's name!
$hash_ref{MAIN}{ZOP}{Dev} = undef;
$hash_ref{MAIN}{ZOP}{Con} = undef;
... # etc

##</code><code>##

sub ixhash {
     tie my(%hash), 'Tie::IxHash';
     %hash = @_;
     return \%hash;
}

##</code><code>##

use Tie::IxHash;
tie %hash_ref, 'Tie::IxHash';

%hash_ref = (
             'MAIN' => ixhash(
                        'ZOP' => 
                            ixhash(
                                'Dev', undef, 
                                'Con', undef, 
                                'Test', undef, 
                                'Exit', undef, 
                                'New', undef ),
                        'AP' => 
                            ixhash(
                                'Dev', undef, 
                                'Con', undef, 
                                'Test', undef, 
                                'Exit', undef, 
                                'New', undef ), 
                        'Exit' => undef,                             
                    )
             );