You could use dualvar and a hash...

use Scalar::Util qw(dualvar);
my %Error=(220=>"Cannot connect to service");

sub mysub {
  if (@_) { 
    return dualvar(0,1);
  } else {
    return dualvar(220,0);
  }
}
my $x;
$x=mysub() or die $Error{$x};
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Of course this still leaves the problem of where to put the error, in the return or in a global. I think your options range from using something like $Pack::Error (which is IMO infinitely preferable to using the magic global $_), using $@ or using something like ${^MYERROR}. For instance I think the following is a reasonable approach:

use Scalar::Util qw(dualvar);
my %Error=(220=>"Cannot connect to service");

sub mysub {
  if (@_) {
    $@=dualvar(0,1);
  } else {
    $@=dualvar(220,0);
  }
  return $@
}

mysub() or die sprintf "%d %s",$@,$Error{0+$@};
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Assuming that you dont have any eval checking logic that this will interfere with (and im not seeing immediately how that could happen anyway) then it should be ok.