Going to the ticket office and pleading your case is the best option. Which means, unless you live in Dallas, New York, Miami or Fort Lauderdale, your friend would need to go to office in his country.

Even then, there's no guarantee they will do this, but ticket offices tend to be easier to deal with than phone agents IMHO. They would have to waive the fee and absorb the fare difference. This doesn't happen often, but its worth trying.

Keep in mind that you are asking a favor from them, so be as pleasant as possible when asking. They are under no obligation to do this, and they would have to go out of their way to get the approvals to make it happen.

Edit: agree with beerup, the sooner you do this the better, within 24 hours stands a much better chance.