Using a straw helped us teach our son (then 6) to swallow pills right down. It has something to do with the shape the mouth makes with a straw and sucking.
Here are some more strategies to try too. Ultimately, getting him to swallow pills would make life easier for all it sounds like.
ADDitude Community Moderator, Author & Mentor on Parenting ADHD, Mom to teen w/ ADHD, LDs, and autism