It seems like what you are talking about is a progressively worsening latex allergy, right? The sort of thing that can kill - one of my close friends died of it. She developed latex sensitivity while a hospital nurse in the '80's (as did many others due to contaminated latex products common at the start of the AIDS epidemic due to shortages) and then died at home where it turned out a plumber had contaminated her new faucets with latex tape of some sort.

So you have a choice in restaurants: be discreet, and possibly die, or politely but firmly ask for accommodation. I'm an expert at that: I'm latex sensitive and both my son and I are gluten intolerant. Yes, it is an incredible pain to ask for the manager (always a manager, never the server) to see to it that your food is handled a little differently, but how does that compare for embarrassment factor to having an anaphylactic reaction during lunch?

I start my request no later than the maitre d's desk, and try to speak quietly on the side to the manager then. More than a few times we have walked out of a place because the manager didn't want to accommodate us. Then we take our $$$ elsewhere. If I have particular concerns about a place, I will try to call ahead for a manager. When your client picks the place, perhaps you can't do that, but you should always be able to say "I have an allergy, and I'll need to check with the manager when we arrive about working things out."