I have been playing with my Aneros for more than 6 months now. For most of the time, no success. However, today, I tried a different position (standing up), and rotating it with my left hand. Suddenly, I felt it hit something, and have the sensation of wanting to pee. I continue for almost 1 hour, and everytime, as the sensation intensify, I clench my butt, and the feeling goes away. I have to "force" myself to relax, and after about an hour, I came without touching my cock (not a lot, just a little cum, about the size of a dime). It was a very strange feeling, but good.
Like some people here have mentioned, it takes lots of practice and relaxation. I am definitely not giving up, and going to practice more and learn to relax.