sub mycmp ($$) {
  my ($first, $second) = @_;
  return 1 if $first ne ( mysort($first, $second) );
  return -1 if $first eq ( mysort($second, $first) );
  return 0;
}
# and elsewhere
  ... sort {&Whatever::Package::mycmp} map ...
# or put in in a variable
  my $cmp = \&Whatever::Package::mycmp;
  ... sort $cmp map ...
# of if you don't mind a speed hit and don't trust the user
  my $cmp = sub ($$) {Whatever::Package::mycmp(@_)};
  ... sort $cmp map ...