Do you know how to?

take a single edge razor blade and wedge it between the plastic and the metal connector. Work it back and forth, then twist to pop it off. A thin knife edge will work too.

Makes you wonder who the "brilliant" engineer was who designed that part.

I think I just remembered how I got them out. Try spinning the binding post nuts all the way counter clockwise until they actually come off. They won't be flush anymore and will no problem to pull with your fingers. If that doesn't work, just find a way to rip them out. You really can't hurt anything.