I was really worried around that age that preschools and daycares would not take my son because he was not potty trained. Fortunately, the places in my area seemed to expect to be working with kids around that age on toileting. If it's a preschool program through public school and you have a formal diagnosis, they still have to take your child. After-school care programs were the only things not being potty trained kept my son out of. My son is not high functioning. Honestly, if it were me, I would buy an unattached switch at a hardware store and allow him to play with it while he sits on the toilet. If it really engages him, it may help. Sometimes fixations change with age and get replaced with different fixations. Good luck with everything.