First of all: great question! We can't always control the environ in which we get feedback. I have 2 suggestions:
One thing I do is get people to write a few reactions privately on an index card and turn them in anonymously. You might persuade your supervisor this would be a good addition to the routine and then offer to bring the index cards and put the questions you want on them. What would you tell someone who wasn't here about what I said?
You can do practice outside your lab (which I recommend as your lab knows so much they are a biased sample). For these practices you can get feedback however you decide to since you are organizin…
How can I get this type of feedback when my supervisor runs practice sessions and this is not at all what he does?
Feel free to ask questions here. Happy to talk further.