Board Thread:Support Requests - Getting Technical/@comment-25793496-20140621163544/@comment-5454372-20140621165855

The info in this page should get you halfway there. That will display the username of whoever's viewing the page (you'll need to install the associated javascript, which is included in that version).

As for making it display it on a click...adding some extra lines of javascript *may* do it, but I'm fairly new to that myself, I'm afraid.