davorg, I did mention I tried to do it with Tie::StdHash :). It's obviously the way to go if one was to choose this method. However, I still can't get a working example going, even using your example above. For me it gives an error when I try to tie the hash...

Can't locate object method "TIEHASH" via package ...
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the line being

tie my %hash, 'ExpandingHash';
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and I also tried

tie my %hash, 'Tie::Hash::ExpandingHash';
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