That's not too hard to do:

print for map{ 
    my( $n1, $a1, $n2, $a2, $value ) = unpack 'N A4 N A4 A*', $_;
    "{$n1.$a1}{$n2.$a2} => $value"
} sort map {
    my $key1 = $_;
    map { 
        pack 'N A4 N A4 A*', 
            split( '\.', $key1 ), 
            split( '\.', $_ ), 
            $hash{ $key1 }{ $_ }
    } keys %{ $hash{ $_ } };
} keys %hash;
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but it does introduce a limitation.

As coded above, the character part of the keys is limited to 4 characters each. They can be shorter but no longer. If this isn't long enough, you must adjust the formats ( 'N A4 N A4 A*' ) to say 'N A10 N A10 A*' for up to 10 chars, in both the pack and the unpack.