I couldn't get on subload in Dubai once. The guy told me if I held a Cat C ticket I could, though. I told him there weren't any available for that day's flight. So he had me go over to one of the computers, find the same flight a month or two down the road where a Cat C WAS available, book it and bring the receipt back to the counter. So I did that and he put me on.
Don't know if that would still work but I guess it counts as a trick!