One word for ya...Impossible! Although doing chest exercises (with weights) can assist in the "perkiness", there is no exercise than can increase bust size. (that was a myth...The whole "i must I must" fad) exercising actually can do the opposite...Exercising helps one lose body fat, and breast tissue is mainly comprised of fat...So with exercise, breasts can lose size, not gain. But, as her boyfriend, you should just reassure her that you like her just the way she is, and that she should be happy with what she has.