Im unsure exactly what "puffy nipples" are and what about them you are trying to achieve. I can tell you that they make a product called blinders that you put over the area under your bra that can help conceal the problem of when they react to temperature and other stimuli. (Please to anyone who may feel offended I am sorry and not trying to be dirty. We as women know that sometimes these things can happen and its embarassing esp when wearing a tighter shirt). Another thing that may help is a botox injection around the area. Botox they are finding now can do more than just erase wrinkles on the face. It is actually an approved treatment for some diseases. You should talk to your doctor or OBGYN to see if that may help. Good luck to you ;-)
You can start by changing your diet and exercising more. Make sure that you get rid of junk food from your diet. Another alternative would be surgery, though you will have to consult with your doctor first.