One possible solution (other than modifying the Tk module) is to use the technique you're thinking of with the

$Home = $ENV{'HOME'};
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statement. Keep a few things in mind:

your $Home will be in your namespace (probably main), while Tk's is in the Tk namespace, so you'd have to do something like this:

  
  $Tk::Home = $ENV{'HOME'};
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your code (probably) won't get executed untill after the Tk module unless you surround it in a BEGIN block, like this:

BEGIN { $Tk::Home = $ENV{'HOME'}; }
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The best thing to do is probably to do as already suggested, get the newest version of Tk, and fix and submit the patch if necessary.