N.B.
This is a need that he is going to have. Period. I know that it isn't something you can make him stop. So I suggest you get his IEP team to address this issue and get an aid with him so they can redirect him or give him something to touch that is appropriate. Teaching him how to touch in a good way is okay too.
I had to work with a certain young man that like giving hugs a bit too much, full on frontal hugs with too long of a connection were uncomfortable even for close friends.
I spent training hours with him on side by side hugs, touching the shoulders and grasping a little tiny bit tighter. I worked with him on job skills, household jobs like doing dishes and laundry, writing numbers and basic math skills so he could understand money better, and how to interact with people. I spent about 5 hours a week with him through my job.
He learned over about a year of weekly training hours and to this day he still knows what is acceptable with family hugs, friend hugs, and compassionate touching.
I was an HTS, Habilitation Training Specialist. I worked in a business that served people of all ages with developmental disabilities. I worked in almost every aspect of this career. Aids in the school system probably won't have the training I did and know all the ways of retraining someone so even if he does get an aid to be with him during the day he still needs to work with someone through an agency providing services for developmental disabilities so he can receive specialized services developed just for him.