I'm uncertain how FreeTDS handles this, but the following should work:

$sth = $dbh->prepare("
declare \@ret numeric
exec TEST \@results=@ret
select @ret
");
$sth->execute;
do {
    while($d = $sth->fetch) {
        print "@$d\n";
    }
} while($sth->{syb_more_results});
[download]

(with appropriate error handling, of course).

Michael