Tracking an iframe on a 3rd party site

Hi, I’m really sorry if this has been answered somewhere else but I haven’t been able to find an answer to this question…

A Drupal site I’m working on has JS code for other people to use on their sites which results in an iframe displaying headlines, see:

I’m wondering what is the best way to add Piwik tracking to these iframes and are there any pitfalls I should be aware of?