Can we join in mixed dhikr knowing that it is bid'ah but not participating in it?

If you are a just sitting there without taking part of it, you are not sinning, but encouragement to the bid'ah. However, if you are a person whom others look up to, then even sitting there will make them do that, hence it is not a good thing. There are limits, one cannot join a Christmas party and say he will do dhikr.