you could do what they did on the 80's playfields where you could drill out the hole in size to suit a nut insert and then the post / bolt just screws into that. Bally did it on high impact posts of the top lanes, slingshots. They also installed a small screw to lock that insert in place as well.

just make sure before you start any drilling of holes that you make some sort of drill stop so you can only drill so deep as it won't take much for the drill to pull itself right through the playfield.