Thats easy to do using a strong mechanical (electric) vacuum pump & the right kind of attachment that's applied to your nipple. You have to do it twice a day for about 10 minutes/each nipple/each time & it really stings at 1st. Two weeks max for very significant new nipple growth. The longer nipples you get are permanent so you have to give it serious thought before doing it. The more you do this the longer they get. Real long if you want - but I wouldn't get carried away like that. You'd be forever tortured and titillated - no pun intended - for instance, by how the fabric of your shirt brushes against them when you move.
I like mine but I cant go topless at the beach now! I get too many stares - makes you feel like a freak - very embarrassing. I also have to turn away n change my shirt fast in the locker room at the gym - and hang a towel round my shoulders thats strategically situated to cover my nipples when walking to n from the shower stall. Stuck with em now. Still...for me... it's worth it! Feels great.