Works best for me in you 2nd position. My 3rd (ring) finger keeps the bugger from going too far astray, but it still can wander. I try to hold it close to the 'fixed' bone with that finger. If I just hold it so the flappy bone is about 1/3" from the fixed bone when my hand slowly turns so it's on the bottom, and touching when it's on top.

Other than that, it's like anything that requires repetitive movement without much thought: just keep repeating it, and try to relax.

I still suck, but I can get the sounds.