Sy there is a product that people use for echinacea plants to trigger branching in the plant. Some people use this same product to trigger offsets. I can't remember what it is called, but there is something out there for sure!
I am not sure that anyone on here who tried it had much success. I do think that good full light, and enough water but not too much, are things that help! Also where you are is beginning to get colder, and I don't think they'll offset as easily in cold weather. Come spring it is likely those other chicks will catch up with the one that offset!