Personally, I would create an anonymous subroutine that knows the correct hash to use. I think the fancy term would be "currying":

my @list = (qw(
    a b c d e f
));
sub by_score {
    my( $score ) = @_;
    return sub($$) {
        my( $a,$b ) = @_;
        warn "$a / $b";
        $score->{$a} <=> $score->{$b}
    }
}

my $by = by_score({ a => 5, b => 4, c => 3, d => 6, e => -1 });
print join ",", sort( {$by->($a,$b)} @list );

$by = by_score({ a => -5, b => 4, c => -3, d => 6, e => -1 });
print join ",", sort( {$by->($a,$b)} @list );
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I'm a bit unhappy with the (lack of) syntax that prevents me from inlining $by. I would have liked to write something like:

$by = by_score({ a => -5, b => 4, c => -3, d => 6, e => -1 });
print join ",", sort( $by, @list );
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... but that's nothing that Perl likes, as Perl doesn't know whether $by should be part of @list or not.