I found with learning difficulties that sometimes a tri-wheeler/wheeled frame is useful initially- as long as you don't think he will be dependant on it? I work in learning difficulties and find you really have to tailor the treatment to include things they are interested in and understand- as they are not always understanding of why their confidence is decreased. If you have someone that works with you, have them control the frame in the front and ask him to walk initially with assistance of one- letting him know that the frame is there but he must try not to grasp it- sometimes making it a competition works (1 point for every step taken without holding on, and -1 point for grabbing the frame for example- or just counting how long he can go without holding it on) with lots of very positive encouragement.
This will be a good one once you crack it!