I know what you mean. I know how to drape, of course, and I would if a client asked, but when he foregoes the towel I leave for him, (men almost always do, or they throw it off during the massage), then he can experience the freedom of letting it all hang out.
Eight times out of ten my clients bone up during a massage and arch their hips hoping to be touched. I will gently put my hand on his sacrum and tell him to relax, and to assure him I'll move my hand to his gluteal cleft and hold it there assuringly before I continue massaging. Often I will rework his lower back since he exerted himself arching up earlier. I'll also lift his leg and reposition it wider. If he doesn't move the other, I'll do it for him when I get to that leg. From there I continue massaging and stretching him.
I love seeing a little string if precum hanging when I lift and bend his leg like in the photo. It's also very nice to see the little pool of pre gathered on the table when he turns over.
Sometimes a client is erect when turning over. Other times, I will have relaxed him to sleep. But the traces of his excitement are always there. I love massaging and being massaged.