It could be if they happen to have the DDE card.
When we were there in Sept my D-I-L wanted to eat at San Angel Inn, even though we had told her it was really bad. I didn't want to waste a TS there, so we decided to share and then order drinks and the fundido seperately using my DDE card. We were told we could not do that, so I said fine, let her order her meal and I'd order the fundido and drinks for my meal seperately. Again we were told we couldn't do that. The waiter finally got a manager who said the same thing 'only one discount/table'. When I told her we had been doing it all week without a problem, she said she understood the rules and all the other restaraunts were wrong. I then asked her what if my son and D-I-L were on the dining plan and I was not, but I just happened to meet them there for luch, would I still not be allowed to use the DDE card and she hesitated for a minute, then folded her arms and smugly said 'that's right, only one discount/table'.