My question is: How are you supposed to regulate eye contact with obviously physically disabled people, and regulate looking at them in general in order to give them proper respect?
I can totally relate - I have had the same problem of wondering if I'm looking at them in a way so as to not seem like I'm staring at them or disrespectful. I can't do it with non-disabled people, so it's no surprise I can't do it with disabled people either. But since what you're probably talking about is just walking by people, it really doesn't matter since it's not like you have a relationship with them.
But if you really have an affinity for disabled people, why not work or volunteer in a place where you can get to know them? Then you can develop a relationship with them and they will know you respect them.