jimi, I have what are referred to as "shy kidneys," too. I have a difficult time providing a sample when I go to regular doctors' appointments. It's like when I'm given that cup and told to produce, my urinary system shuts right down. And that's when I can go into the bathroom by myself and shut the door! I can't imagine having to go in front of somebody.
(I've tried running the tap water, even, to give a hint to the bladder.)
And, yes, I have had some nurses be downright hateful about it! That sure doesn't help any!
Maybe since this issue might be a matter of not being able to take Ritalin any more, then maybe you could talk to a doctor about it. If you find out something that can get the flow going, then please let me know!
By the way, I am sometimes successful when I drink a lot of liquids a couple of hours before I go and just hold it in until I get to the appointment, when I am desperate. Also, the soda called Mountain Dew tends to run right through me. I think I'd be able to go after drinking a bunch of that if I were even given a pot and told to pee in front of the entire world!