How about something like this:

    package Tie::HashNKeys;
    use strict;

    sub TIEHASH {
        my $class = shift;
        bless {}, $class;
    }

    sub STORE {
         $_[0]->{ join $;, sort split /$;/, $_[1] } = $_[2];
    }

    sub FETCH {
        $_[0]->{ join $;, sort split /$;/, $_[1] };
    }
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Sample:

    tie my %hash, 'Tie::HashNKeys';
    $hash{'csUsers','csGroups'} = 'foo';
    print $hash{'csGroups','csUsers'};   ## prints 'foo'
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Is that kind of what you want?