Update: I forgot about the magic aliasing power of @_. See Corion's branch in this thread.

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I believe part of the problem is that $array[$x] is not a lexical. Consider:

my @data = (1 .. 5);

{
  local $data[2] = 100;
  print_data();
}
print_data();

sub print_data {
  print "@data\n";
}
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(Did you know you can use local() on elements in lexical aggregates?)

But moreso, because the elements in aggregates do not have symbols, I do not think they can be aliased. I would expect Perl 6 would make this possible.