You can't. That's why I would suggest a Multi Stage feed such as Flock Raiser.
This is what I do as well. It's the best suitable for method for both sexes in my situation.
Sorry but I don't just go on the word of a company. There purpose is to make money off us buying their feed not the well being of our birds. If you search here on BYC you will see several threads explaining the damage caused by excess calcium.
4 month olds should NOT be on layer pellets. That is too much calcium for their bodies to process. Do you have flock raiser in your area? That would be your best bet.