I would not do it and you will probably find a lot of good contractors that would not touch it with a 10' pole. Cement board and a "waterproof" sealer and membrane, especially when it comes to the frost movement you can get in your area.
You apparently are not under a code, but if you ever go to sell, any reasonably imtellegent home inspector should spot that. Just because a code is not contolling now, that has nothing doing when you go to sell.
How does a wood frame wall enter into a patio installation? Is the patio above aliving area?