Wish I could help, but I'm not good at expressing anger. The couple times I've expressed anger in the therapy room have been toward my T, and they haven't gone well... I guess I did express a bit toward my mom at one point, and that went OK, but nothing that would be helpful to you, I don't think.

For what you planned to do, I'm not sure if this would be safe enough or have the same effect, but could you put the plate in a Zip-loc (zipper-sealed) bag and smash it in there? (not sure if smashing it would force it open though). Or, say, in a trash bag that's tied closed? Mainly mentioning the Zip-loc because it's clear, so you'd see the broken plate. But if you put it in some other sort of bag, you could open it after (inside, away from the wind) and see it maybe? Or if you have clear trash bags there.