Hey, frequent visiter, posting for the first time here. I know this is already posted on BBW chan, but since it hasn't been mentioned of yet, I'll post links and stuff to it here. I also wanted to contribute something to the community here, since I've gotten so much from it already. This isn't mine either, and I'm not sure who it belongs to, but that's the way the internet works sometimes.
It's a poser (I think, correct me if I'm wrong) story about a guy who goes on a blind date, and eventually finds his date can grow in size when aroused. It follows the natural progression of things at that point. It includes breast expansion as well, but I feel it fit better in this area.
Link to the topic at BBW:
http://yum.bbwchan.org/size/res/2689.html#i2689
Link to the download:
http://www.otaku-hosting.nl/erinstory.rar
Edit: Better sized picture below.