drop gravity javascript onto site -ab controlled

Gravity are a third party recommendation service who we' d like to check out. This drops their a snippet of their code into our DOM and does their tracking for them. I want to A/B test this and, once the code is in situ, to use their api to populate the right-hand-mosy-popular component( badly outlined below ), so that we can see how the clickthrough rates compare. 
![dog-article](https://f.cloud.github.com/assets/986155/1985811/243e27fa-8444-11e3-8d28-084d4ad3631b.png)