I had originally posted this solution on the XBMC website, and XBMC member Livin kindly recommended that I share the post with the Eventghost community... I hope that this helps some users!
After unsuccessfully testing several different methods of killing the "sponsored session" popup box from TeamViewer, I worked up a quick macro in EventGhost to do it automatically. I'm not all that proficient at EventGhost, so this probably isn't the cleanest solution, but it appears to be working for me.
Here is a quick screen shot of the event tree that I created. I did have to add a plugin "ProcessWatcher" which can detect when the TeamViewer desktop session is destroyed. I used this event to trigger a macro to find the TeamViewer popup window, bring it to the front, and then send the {Enter} key to the desktop.

I created a simple xml tree from EventGhost of the macro, but I can't seem to figure out how to attach a file to this post...
Hope this helps some of you.
Thanks!