Suggest Remedy For Chronic Constipation In Cerebral Palsy Patient

My 17yr old son has cerebral palsy.Wheelchair bound. Years he has had constipation problems,some causing severe dehydration. Laxatives only do so much and leave some upper blockage. Same w/suppositories and enemas. My sons muscles are weekend now and can t help push out bm when we manually remove BMS.As of now we are back in the hospital for 2 days and again no movement. Any help/suggestions. Please help my little man,he has enough issues to deal with.