Certainly not no discount for anybody! There are a couple of options.
One is to get a second card and split the party into two groups. It's unlikely that you are going to be able to seat 11 together at many restaurants anyway, so that may be a workable idea.
Another idea is to just take your chances. There have been anecdotal reports of servers applying the DDE discount to more than 10 people -- even up to 12-13, I believe.
Personally, I think I'd go for the second card and be done with it.
Worst case scenario, you're going to lose the 20% discount for only one person...so that's not the end of the world. You're still going to be saving a princely sum.