Does he say anything? I don't know if this would help in the least but this is what I did with my son, he's much younger and more verbal but I figured I'd throw it out there anyway. My son started out only saying letters and numbers, he'd scream them at me like they had deep meaning. So I started putting his toys in different containers that each had a big number on them and put them in sight but out of reach. He learned which toys were in each container so instead of asking for his magnet letters he'd ask for number 5, or 6 for his cars, 1 for play food, ect, ect. I just took what he could say and assigned meaning to it.