To follow up on my earlier post, I did ultimately get credited for my egift card purchases. I figured if they were denying the charges because of what they were for, then they could just come right out and say so. So after the three weeks were up, I sent another message. I got a very brief, polite response from a rep apologizing for the credit not clearing already and that he would go ahead and credit my account.
Because of the language used in the messages, I got the feeling that they knew I was trying to get away with something, and that they'd let it go this time, but the jig is up. It's possible I'm being paranoid.
I am planning to switch to another airline with more options for using the credit.