Hi.
I know where you are coming from. I used to work with a woman who was diabetic and she was a nightmare. When she started the job she knew there was a shift system, but she flatly refused to do it saying it would interfere with her diabetes. We had fairly regular 10 minute breaks but she would spin hers out to 30 mins, saying she needed to eat more because of her condition, etc etc. We ended up having to "carry" her most of the time and felt resentful. She was one of the reasons I left. I didn't mind doing my job, but I objected to doing half of her job as well.
You are on a hiding to nothing with this one as he will play the disability card and scream "discrimination" at every opportunity.