Number 2 may help in terms of advice - but it's still the people involved who will have to step up and act.
Number 1 sounds like a form of shunning, and it's exactly the kind of passive aggressive response that's popular in many places, but which I strongly dislike. Whatever happened to just talking directly to the people involved?
The former sempai's advice is much more valuable than ours because he (or she) knows everyone involved and the dojo's culture, everything that we are ignorant of. So his advice might actually be applicable to the situation and practical.
I think that qualitatively and quantitatively, boycotting someone's classes is not shunning. But it would be hard to boycott his classes and then work with him as a classmate. So I see your point.
I figured I would run my suggestions up the aiki flagpole and see if the anonymous posters would salute.