You can actually pass the hash of arrays by value without any problem, as if it were a single-dimension hash (in a sense it is a simple hash in which the values happen to be array refs):

$ perl -MData::Dumper -e ' my %h = (tim => [ 4, 7], joan => [5, 8], fr
+ed => [8, 3]); 
> proc(%h); 
> sub proc { 
>     my %h_sub = @_; 
>     print Dumper \%h_sub;
> }'
$VAR1 = {
          'tim' => [
                     4,
                     7
                   ],
          'joan' => [
                      5,
                      8
                    ],
          'fred' => [
                      8,
                      3
                    ]
        };
[download]

Now, of course, this implies copying the (top level) hash. If it is large, you might want to use passing by ref to avoid the overhead of making such a copy. But the structure of the data does not prevent you from passing the hash by value.