I just happened to come across a thread at flyertalk today on this subject. The consolidated thread is here:
http://www.flyertalk.com/forum/showthread.php?t=825506

I haven't read the thread but it should have some helpful info.

I would call the airline to see if you could go to the airport with your id and specifics about the reservation and have the passenger record notated to not ask for the cc at check-in (or have the flag that tells the checkin agent to check the cc removed from the res). You could put it on hold and go to the airport to buy it.

You have 24 hours from buying the ticket from UA to get a full refund.

Just discussed on the DL forum at FT today too http://www.flyertalk.com/forum/showthread.php?t=769610

Hello,
Had this problem when buying a ticket for my daughter on South African Airways. She was in SA with no computer access and needed a ticket. I took her cc info, and bought her ticket through SAA. When she went to airport she DID have to show her cc in order to get on the flight. There was no problem because the info matched the purchase.

Purrcy, this is such a simple, wonderful, easy to follow idea! Thank you!!

I wonder also, maybe a travel agent can help in this case? Maybe this is one of those rare instances when it pays to pay for service?

The credit card can be a form of payment and can be form of ID unless the eticket is not paid for by ccd in which case it can be something else eg passport/national ID/frequent flyer card. The ccd used for payment is not always required on check in and is dependent on the requirements of the airline. Maybe it is not a requirement in the US but it is in some other parts of the world.

You can google this subject for more info.

The original question was about purchasing the ticket in the US for a flight originating in Brazil for someone other than the ccd holder; should be possible on a site like Travelocity.

I bought my brother-in-law a OW ticket from CDG to LAX using my FF miles, no problem (no I wish I'd hoarded those miles as Paris calls!!). We have many times bought RT tix for my mother & father-in-law and have never had any problem at all. The e-tickets make this all so easy. Just be sure to enter the reciepeint/passengers correctly spelled name and be ready with other info they might ask for ticket purposes (DOB, maybe?).

It's really no big deal.