Check out these exercises. I know somebody that has used exercises found in second link and it really works:
Exercise for Firm Breasts: Chest Workout for Women -- with Dumbbells
Chest Exercise for Women - Exercise without Equipment
Do 10 of each SIMPLE Breast Exercises
Follow instructions on Breast Massage - Growth, Shape, & Health
Finish with Breast exercises - 5 SIMPLE EXERCISES to firm, lift, and shape