Basically, you're trying to circumvent the rules to get a cheaper fare. I wouldn't expect US or any other airline to go out of its way to help you. (Not passing judgment on what you're doing, just saying what will probably happen.)
If you bought a one way ticket as you stated, why not just reprice the ticket for the destination you want? You may end up with either a refund or a MCO available for future travel (the latter if the ticket was nonrefundable).
[This message has been edited by USFlyerUS (edited Feb 03, 2004).]