In a module of mine (might event release it at some time), I needed the same functionality, so I wrote:

my $caller=(caller(1))[0];
no strict 'refs';
 @out=sort {
      local (${"${caller}::a"},${"${caller}::b"})=($a,$b);
      $sort->($a,$b)
      } @in;
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This might not give the fastest runtimes, but allows the user to pass a compare sub that works in any of the two ways.

-- 
        dakkar - Mobilis in mobile