There is no protocol for this, and it is not that extraordinarily uncommon. Your friend probably fine and just needs to accommodate the low bar position. He does not require stretching in PT. If he wants to low bar, he needs to perform the Horn Stretch explained in a video on this site. Training is going to be hard and uncomfortable, and if this is his first time doing something like this, make it as easy as possible. Start extra light and set the expectation that it is going to be sore. You want to reduce the fear surrounding the sensations following training.