I can't be sure but to me it looks like the weights holding down his balls are more or less resting on the towel. I think while they are "at rest" he is sitting quite hard on the wedge and the dildo is somewhere up his ass. To get relief he has to straighten up on his tip toes but that would be painful on his balls as those lock boxes will probably be full of something.  Also he has to keep his legs apart on those stools for obvious reasons.