You don't need to individually shared the hash elements. You only need to ensure that the hashes are shared before you assign anything to them.

Here's a quick demo:

#! perl -slw
use strict;
use threads;
use threads::shared;

sub test {
    my $href = shift;
    for( 1 .. 10000 ) {
        for my $ref ( values %$href ) {
            for my $value ( values %{ $ref } ) {
                $value++;
            }
        }
    }
}

my %hash : shared = map{
    my %hash2 : shared = map{ $_ => 0 } 'a' .. 'd';
    $_ => \%hash2;
} 'A' .. 'D';

threads->create( \&test, \%hash )->detach;;

for( 1 .. 5 ) {
    lock %hash;
    print "$_ => [ @{[ %{ $hash{ $_ } } ]} ]" for keys %hash;
    sleep 1;
}
__END__
P:\test>thr-hash.pl
A => [ c 0 a 0 b 0 d 0 ]
B => [ c 0 a 0 b 0 d 0 ]
C => [ c 0 a 0 b 0 d 0 ]
D => [ c 0 a 0 b 0 d 0 ]
A => [ c 3447 a 3447 b 3447 d 3447 ]
B => [ c 3447 a 3447 b 3447 d 3447 ]
C => [ c 3446 a 3446 b 3446 d 3446 ]
D => [ c 3446 a 3446 b 3446 d 3446 ]
A => [ c 6903 a 6903 b 6903 d 6903 ]
B => [ c 6902 a 6902 b 6902 d 6902 ]
C => [ c 6902 a 6902 b 6902 d 6902 ]
D => [ c 6902 a 6902 b 6902 d 6902 ]
A => [ c 10000 a 10000 b 10000 d 10000 ]
B => [ c 10000 a 10000 b 10000 d 10000 ]
C => [ c 10000 a 10000 b 10000 d 10000 ]
D => [ c 10000 a 10000 b 10000 d 10000 ]
A => [ c 10000 a 10000 b 10000 d 10000 ]
B => [ c 10000 a 10000 b 10000 d 10000 ]
C => [ c 10000 a 10000 b 10000 d 10000 ]
D => [ c 10000 a 10000 b 10000 d 10000 ]
[download]

Far from ideal I agree, but there are other parts that are much more broken than this.