From 5.22.0 onwards:

use feature 'refaliasing';
no warnings 'experimental';

my ($x, $y, %h);
\$h{foo} = \$x;
\$y = \$h{foo};
$x = 99;
printf "%d %d %d\n", $x, $y, $h{foo}; # prints 99 99 99
[download]

Buts it's of course still an experimental feature.

Dave.