Personally, I would stop every member of the charity ride and explain to them that by wearing helmets they were contributing to the myth that cycling is such a dangerous activity when compared to walking or driving that it requires a helmet.
I would berate them for discouraging people from cycling despite all the evidence that cycling increases your life expectancy in the face of the data showing that making helmets compulsory, as in Australia, reduces cycling numbers and even encouraging people to wear helmets, as in Denmark in 2008, reduces the number of cyclists.
I was a bit busy this weekend unfortunately.