The comment by Beth above reminded me that a lot of my daughter's OT revolves around oral motor exercises, which is supposed to help her with language development, and I have to admit she is speaking a lot more clearly since therapy started. We started out by purchasing an electric tooth brush and using it to brush her teeth twice day. Then we started playing little games with it, like holding it about a half inch from her mouth and seeing if she could touch it with her tongue. Then when she could do that we would move the toothbrush to different places to see if she could move her tongue to the left or right. I'll never forget the day she was able to lick her upper lip. Any little fun things you can do to get him to work is tongue will help him with speech development in the long run. Some other things that will help with speech are sucking thick liquids through a straw (yogurt, oatmeal, applesauce), having him blow bubbles or whistles, chewing gum or teething rings if he's not ready for gum.
Also, I recently read this blog written by a mom whose child is in similar circumstances. Maybe it would help. Good luck!
http://www.spdbloggernetwork.com/2012/08...y-excited/