If you're convinced it is feather picking, I really would try to increase dietary protein as well, in all honesty. Even with the prepared layer feed, a little extra additional protein can really help them out and can reduce or even stop a feather picking problem. (And they will totally love scrambled egg and tinned tuna, if they're anything like my lot!)
It won't hurt to try anyway... good luck x
It won't hurt to try anyway... good luck x