It occurs to me that the only way to encourage that effectively is to have another feedback system like "social ukemi". Juniors in general should be the people with less power and therefore their combined feedback should be a more accurate gauge. (If someone is not being too compassionate with me and I have a ton more power than they have I really might not notice all that much.) Aiki power is the ultimate leverage. People who are going to be jerks, will have to train themselves to stop outwardly displaying their jerkiness if they want to attain more "power".
The grad students I supervise have given me an interesting perspective on this. We have a small subset of faculty members who are, in a phrase, hard-asses.
Every semester, I get a number of verbal complaints (or if not complaints, just students stopping by to ask why so-and-so is an egomaniacal, demanding pain-in-the-arse). At the end of the semester, students fill out faculty evaluations.
Then, at the end of the year, the students all go away and intern in professional practice. Inevitably, when September rolls around again, the same students who were complaining in the previous school year are telling me that they've come to a new appreciation of so-and-so, whose forceful insistence that they absolutely needed to know x,y, and z cold or they needed to find a new path in life proved to be dead on, and prepared them for their professsional internship training to an extent far greater than any of the warmer, fuzzier, kinder, and more apparently compassionate faculty members they had liked better at the time.
What I take from this is that in order for such an evaluation system to mean something, it also needs to incorporate a good chunk of time spent in a demanding external experience that will serve as the basis for comparison, and a second look. Without that component, it is entirely too easy for the evaluation system to turn into an exercise in student narcissism that will persistently and consistently drive down expectations and achievement levels.