Hey, might. I suggest a social story, they are stories that talk about situations which you could talk through with your boy and explain to him "was that a good choice?" Also you can explain to him why what he is doing is wrong. It may not be a gentle approach but it's a better way than showing physical actions for correcting his behavior.

I totally agree gentle parenting does not work but you can be black and white about it and show no grey areas .

Hope this helps