Adding wood inside the bed probably won’t do much. The research I linked to in this and other articles indicates that chemicals are only a worry very close to the edges of the bed itself. My best guess is to grow your veggies several inches away from the edges of the pressure treated wood. The new pressure treated wood doesn’t use the same chemicals as the older stuff, so it shouldn’t be as big a deal as it was years ago. Most of my beds are of pressure treated lumber. Good luck.