I finally found a solution that works with Word 2013. In Word 2013 Review ribbon, set 1) Tracking to either "simple markup" or "all markup", 2) click "Show Comments" button if not grayed out. Finally in the Home ribbon, turn on "Show/Hide" or hit CTL*. Voila, the balloons show up to the left of the text! It seems like Word 2013 chokes when there are a lot of comments in the document.