Do you have a long last name? If so (and even perhaps if not), you could just tell anyone who asked that they had to shorten your name to get it to fit on the ticket. I don't think anyone will care, though. Have UA put a note in your PNR, and you should be set. It is very frustrating, but I don't think it'll end up being a hassle.

Also, if you're going to Asia or anywhere else that doesn't use the Roman alphabet, they most certainly won't notice. If they do, they'll probably assume it's an accepted short version of the name.