Lol, he screams when you put plants in his tank?! That's crazy. A plant must have traumatized him as a child, haha.
You should definitely try nightcrawlers if you haven't, I think it's hard for any frog to resist them. If he doesn't like supplements you can do this with nightcrawlers, wait until he has half of the worm in his mouth and then sprinkle the supplements on the worm. He's not going to spit a worm out that's half swallowed, that way he'll get the supplements.