K.L.
This is not a technique, but a bit a good info I wish I had had when my son was young. Potty training is a developmental skill, not a learned skill. I studied anatomy and physiology after when my son was older and learned that, normally around age 2 1/2 to 3 1/2, there is a developmental stage in a child's hormone/neurology that provides the child with increased genital sensitivity. This increased sensitivity allows the child to be less comfortable with soiled or wet diapers/underwear.
When my son was 2, I started trying to 'teach' him to use the toilet. I don't know why it never occured to me that if he could learn to walk and talk, 'learning' to use the toilet should not be such a monumental task for him. One day he got up and started running about bottomless in mid diaper change. I decided to let him do that for a few minutes, when he suddenly got a startled look on his face, ran over to me, stood over the clean diaper that was waiting for him, and urinated into the diaper. That is when I realized, "He knows what to do. He just doesn't care." A couple of months later he asked for the Potty Book we had not looked at for months. He took it to be with him and the next morning started using the toilet. It was his idea. Two weeks later he had an accident and was very upset about it, very uncomfortable, and walked bow-legged to the bathroom. I remember thinking, "Two weeks ago he could have sat in that mess for hours without caring. It must FEEL different to him." So, when I learned about this physiological change that is a normal part of development at that age, it all made sense.
So, you may want to start asking your son how the diapers FEEL or how messy diapers FEEL and suggest that he can wear the underwear that FEELS better when he poops in the toilet. Just remember, you can't make him feel the difference. Some kids just experience that development switch earlier than others.
It just seems like pediatrician would better inform parents about these things. How else is the common parent going to know this. I don't know why our children are allowed to graduate highschool without knowing more about early childhood development and the difference between learned skills and developmental skills.