I have had to use a warm washcloth and rub his bottom with it. It's the warmth and movement that help them have a bowel movement. It may take a while but be diligent and he will.He hasn't popped at all. I watch the mom cat and she doesn't lick their bottoms. I have even tried to get her to do it. I got him to poop a little bit using the triangle method and I don't want to risk giving them anything.
It is possible he may have a blockage and is unable to so you may have to give him something to soften his stools so it can pass.