G.B.
My question is one of interest, not condemnation in any way. I have over 13 years dealing with developmentally disabled kids and adults so I do ask with the greatest respect.
Is this something he is ready for? Is he mentally ready for this? Often we found that the parents would just be ready but the individual wasn't. Sometimes they are never ready and just have to be changed always.
It would be nice, of course, if he could do this. Are you working with a team that is helping you? Is the school system working towards this too? Does the doc think this is something appropriate for him right now?
All these are questions I would ask you. I know how hard it is to get peed on. It happened to me tonight.
Our boy with sensory issues was having a melt down and I was restraining him a bit, I have described this action in great detail in many of my answers to moms so if you are worried about how I do that you can check out my method on my profile.
Anyway, he was screaming and hitting, kicking, head butting me, clawing, trying to punch everyone, and I was holding him in my lap. He decided to just let go thinking I would put him down. Didn't work. I had to go take a shower after he calmed down and went to go take his. The chair is not fabric so it cleaned up very quickly.
But regardless of this, he is pretty much potty trained during the day.
If your guy is ready then the only thing I can say is be patient, find some reward that he loves that will stimulate him to concentrate on pushing the urine out. If he has control of those muscles he should be able to push something out by trying. Our guy liked jelly beans and would strain himself to get 1 for pee and 2 for pooh.
It may take years to potty train someone with disabilities but once they get it the joy is wonderful. Good luck.