Oh, I almost forgot: you could also try using the Horizontal Milling's finishing feature - set the Stepover to zero and your Cut Depth to a small increment, and then your Min Finishing Angle to ~60 degrees or so so that it leaves low grades alone and focuses on more vertical wall areas. v1.53a does however generate cuts around the inside walls of the canvas, which are not useful with projects like this, but they can be disabled in the upcoming beta release that should only take another week or two tops. I think this is what you're looking for (except the cuts that it produces around the edges). For now I'd suggest using the largest Cut Depth you can get away with to reduce the time wasted by the inside wall cuts v1.53a generates.
- Charlie