(I am a mello player)
I got mine off on August 11th. I could play low range, and up to A on staff without difficulty. I simply practiced a lot (buzzing, long tones, etc.) and switched from my Kelly to a metal mouthpiece. I did work, playing my entire show an octave down. I did a lot of screaming (on horn and off horn). After a while it just seems to magically work.
Now, August 24th, I can get to E on staff without difficulty, and get up to G right above with a deep breath 2 seconds before. My quality has improved to the point that I am able to play a mello solo in our show better than my section leader (again).