I saw the suction things on the TV along with all the other trials, the conclusion was the suction cups were best but took 6 months of wearing these cups every single night, and were very uncomfortable, there was a small enlargement that soon disappeared when she stopped using them.
The only way is surgery I'm afraid.
Postdog. I assume you know that this poster is not a 13 year old wishing bigger boobs.
you could use toilet paper. Wipe the space between your boobs vigorously twice a day for a few minutes, for say, 5 years, it'll make them grow massive.
I can't prove that's what did it, but it definitely worked on my wife's ass...