Is it possible to mark the message thread with 'unseen=0'?

I work on Google Chrome extension for facebook.

I have a button and if you click on it, a popup with latest active threads appears. I want to say to facebook server that no threads are 'unseen' afterwards. So that the messages jewel on Facebook main page will show no notifications.

Can I do this with Graph API? POST calls to graph.facebook.com/thread_id with unseen=0 don't work.