Would it also make sense to have every harsh interviewer be interviewed by all the other harsh interviewers, and see how well they all perform on each others' question? In each case, incentivize the interviewer to stump the interviewee, but using only the same questions they use in real interviews with prospective candidates, and link the interviewee's performance to their bonus or something. Put the harsh interviewers in the same situation with a similar amount at stake as prospective candidates, remind them that nervousness and the unnatural setup relatively to typical working conditions can also be a factor in interview performance.