Little Dove,
I have been through this, and successfully dealt with it. Let me tell you my solution.
First, what you have done so far is a good start. You have (anonimously) notified the sponsor of a problem. The next move, I propose, is to do what I did.
I was a trained scoutmaster who moved to a new town, and began to work as an assistant with the troop sponsored by my church. That troop was one of the oldest and most respected in the area. It was obvious that the SM had a drinking problem. We never had a problem at meetings (as you have) but it was a very real problem on camping trips. This SM was a great guy, and had been a wonderful influence in many boys lives over the years, so nobody wanted to acknowledge this problem. I found out later it had gone on for years, and people had just looked the other way.
I went to the troop committee and informed them of the problem. It was hard, because every one of them knew and loved him. But I told them that I had witnessed the problem, and was reporting it to them. I told them that, now that they knew, they had the fiduciary duty to do something about it. If they did nothing, if a child was hurt, and the SM's alcohol use in any way contributed to it - or if he had been sober, he could have rendered better aid - they would be personally liable for any damages, and COULD face criminal charges, under certain circumstances.
Within a few days, he was removed. They hated to do it, but none were willing to risk their own homes and savings accounts to protect him.
If this doesn't work with your committee, it should work with the governing body of your sponsoring church - because it will apply to them as well. It is a drastic step. Maybe the lives and safety of the boys are not worth it. No, you have already shown you know the right thing to do.
(By the way, in addition to being a trained scouter, I am also a lawyer, and this doctrine of "respondeat superior" liability is valid in all states.)