How about getting allies? Talk it over with other students. See if you can get more people to coordinate to stand up with you. If multiple people stand up to the professor in a coordinated fashion, it becomes much harder to dismiss the issue as just being you who is unreasonable.
You could address him as a group or meet as a group his superiors. Talk over with each other the strategy.
If others are uneasy to speak up, then just ask for permission to speak on their behalf. The important thing is to get across that you are not alone.