The only helpful think that I can think of, that hasn't already been stated, is that the new dojo 2nd sounds completely unaware that the kohai of the dojo don't like him, and probably wouldn't continue to attend classes if he were to throw a successful coup. I wonder if his behavior would change if he were made aware of this.
Suggest making sempai aware that the other students do not admire his behavior and prefer their senseis approach. I have seen this done in a slightly passive aggressive way by having a meeting at which the teacher asked the "target" student to articulate their position, and then other students responded to it. It was effective. You could be more or less direct about doing this. (personally I don:t think I would set them up first, it feels slimy) But I think its up to your sensei. Have the other students told him/her how you feel? could be a good first step.