Ohmiway... As sadistic as this story is, it's very... Good?? Lol I do love it, even though I cringe about 4739747 times per chapter.
If I may suggest one, I got it from the movie, "Untraceable." there's one scene where he encases this guys lower half in concrete, sets up heat lamps on him and the guy gets these God-awful blisters all over him. Maybe you could do something similar, and gradually turn the heat up until it practically has his blood boiling?
Just a suggestion :)