It sounds like he needs a pediatric impatient facility. Children's Hospital up here in Seattle has one, so I would think that your regional children's Hospital would as well.
That, or home care. (One of my psych profs did that for awhile... Treating in her clients homes, whose disorders precluded them from coming to her office for treatment UNTIL they could be treated well enough to actually GET them to her office OR disorders that were home specific, like PPD induced OCD. Severe anxiety disorders were a common 'cant treat unless they can be treated well enough to come', as well as agoraphobia, etc.
My 10yo is ADHD, and over 5' & 100lbs. Meltdowns are common with ADHD, so I get what you're saying when you say it's physically impossible to move him from point A to point B unless he cooperates. We had a single day of school refusal with PARTIAL cooperation that took 4 hours last year. Every day, all day would be absolutely insupportable.
You need help.
Either 24/7 until he can start cooperating (I almost said 'choose' but with neuro conditions that's like saying 'choose' not to give birth while in active labor... You can't stop your body when it takes over... And the base functions of the brain are just like giving birth, throwing up, breathing, peeing... One can't just 'decide' or 'choose' not to. It has to be physically possible before a choice can be made), OR someone coming to your home to work with him & his inability to leave it.
NOTE: I have no idea on your stance on meds... BUT... Meds are often required to deal with the base brain levels IN ORDER to treat / begin to make something a choice. Meds rarely work on their own, it's a 2 step process of being physically capable AND ALSO learning how to do a thing consciously. You may already be trying different medications, but if not, it's something to keep in mind.