There is an interesting thread, I think in Random Ramblings, about demanding to know what hatcheries feed their breeding stock. The gist is that hatcheries are breeding malnourished birds that are born with protein difficiencies and feather picking habits from day 1. Not a solution to your problem, but one of many possible causes, and an interesting thought.
Mine did not get the pinless peepers until they were 10 months old. I had put up with the leghorn pulling feathers basically for all of those months, but at the end of a long cooped up winter, others began to pick up her bad habit. That was when I increased protein and started letting them free-range a bit for the first time. It broke everyone of the habit except for the leghorn and one Welsummer. They got the peepers.
Both had the peepers removed about a week ago, - the leghorn because of an injury, and the Welsummer because I wanted to see if she was rehabilitated. So far, the Welsummer has not been seen picking, but the leghorn is right back at it, and pretty steadily too. I hope to get the peepers back on her this evening.
The thread I was talking about above was also saying the soy is not the best usuable protein source. I feed a high-protein feed, but I'm sure it must be soy based. Whatever the reason, it only seems to be an issue for this leghorn, and since the peepers worked, they are coming back.
I know people who debeaked to deal with this issue. I'm not condoning that, just throwing all the options out there. I do think they sell peepers in different sizes if you ever pursue that.
Good luck to everyone!