XF 1.2 Using bit.ly custom short domain with AddThis

[mistypants]

I recently enabled AddThis sharing on my site. I already use bit.ly for my Twitter account, and recently set bit.ly up to use a custom short domain. AddThis offers functionality to link your bit.ly account with your AddThis account, and shorten URLs with your custom short domain. The instructions on doing it are found here: http://support.addthis.com/customer/portal/articles/381247-url-shortening#.UvaAUrToidI

I've entered my login info & API key, but I'm not sure where to add the provided code:

var addthis_share ={
     // ... other options
     url_transforms :{
          shorten:{
               twitter:'bitly',
               facebook:'bitly'
          }
     }, 
     shorteners :{
          bitly :{} 
     }}

I'm assuming it's somewhere in XenForo's many files but I didn't know where to look.

Thanks for any help!