1. Before walking into the wall, set up so that you are looking 0.25~ degrees from the center(showpos helps)
2. Crouch walk into the wall and don't move your mouse
3. If the prop doesn't tilt right away you should be good and the prop clips you(or goes through the wall) in the next seconds
4. Usual save/load shenanigans

I don't think the angle matters that much, pretty much just don't move your mouse, look roughly to the center and you should be fine.