SanDiego1K's advice is sound. I've had more than one occasion where I asked to add a second name to the reservation because I was gifting the award, the CSR said they had done it for me, I called back and the second name wasn't there. Don't know why some CSRs have such difficulty doing this.
However I've never ultimately had a problem, I just make sure the person's name is on the res as the second guest.