I have spent so much time trying to accomplish this since setting up my FB store! BUT, the Payvment people did the work and now it is automatically there when you click on the picture of the item!! I was able to add the Pinterest button to the main page though, too.
Just thought I'd share!!
Yay!!! I love using Pinterest, and I'm going to hopefully start selling my stuff online too...so using Pinterest to promote to people I don't know would be awesome!
My Blog: http://anthologybeadgeek.blogspot.com/
My Shop: http://www.etsy.com/shop/AnthologyBeadwork
YAY! I just installed it on my website yesterday