Let the less dedicated participants feel that they have done their part, and numbers will dwindle. As numbers dwindle only the extreme remain, and in few enough numbers that the entire cause is then written off as fringe.
It is a phenomena usually seen when cults start ejecting their more moderate members, but in this case it is harnessed by a separate party.
Exactly if you give people a "complaint department" and a method to file a complaint you put distance between their anger and the thing they are angry about and they will many times cool down and not explore other more viable options (not sure if that is what you meant but it's one of my thoughts about a process like this).
My (probably unnecessary) expansion on this is that when you deflate the sentiment, all those who remain angry will become more extreme (just by nature of not being surrounded by less extreme people) and will become easily to marginalize/fire.
Their first response was to toally agree with us and give us the distinct impression that they were going to "make good". As a result we didn't do anything we just waited because we didn't think there would be any problem in restitution. Well time passed and later I had lost my steam when they finally came around and said "sorry but we're not going to do anything".
Also known as "letting a hundred flowers bloom." How'd that work out for the "flowers?"