This is pretty easy and involves a mind over body technique.
*rubbing lotion (moisturizing lotion is recommended)
First, make sure your chest is clean. Next, apply lotion to your hands and massage into your chest gently. While you are messaging, imagine and feel your breasts enlarging (the mind over body technique comes in). Once the lotion has dissolved, you may add more and repeat the steps if you like. Repeat the method at morning and at night. You shall get results in time.
Also, please tell me if this works so I can find more methods. And a tip to make it more effective is meditating before you preform this so you can focus more.