I know it's a completely different system, but what helped my get to A grade was a good recommendation, and constantly being in the conductor's face.
Dennis was constantly adjudicating events where I'd solo. He saw my potential, new I was from a similar region to him, and kept an eye on me for a while, along with his principal Eb bass player, for whom I had a lot fo respect at the time.
When in year 12, I needed something top push me musically. I was in a statewide wind orchestra based in Brisbane, but like most tuba players, this didn't feel like a real workout. I mean, I could play the euphonium and trom parts to pitch!. My teacher had just finished being a guest soloist on their last christmas tour (every Christmas they go around to some of the smaller brass band towns to do a publicity concert) and arranged for me to travel up to Rockhampton for a couple of rehearsals.
Next year, I appplied for uni in Rockhampton, but I wanted to stay a member of my old band because I felt I'd be going home more often than I actually did. Within a week of mmy application, Dennis found out, and asked me to permit with them for State championships. I agreed, and after a lot fo good feedback with my efforts, I was asked to dual register, or leave Gladstone to join them. Dual registering costs a packet, so I resigned from gladdy and joined the Big League...
so to you, all I can confidently suggest is be active, work hard, and be ready to things for the conductor that his normal musicians won't. It may pay off!