It sounds like you're talking about what forums usually accomplish using the HTML "title" attribute. Doing it in JavaScript lets your bubble be more stylish, and there might even be a way to do stylish bubbles using just CSS (having a separate :hover style or something, with the regular style hiding the children), but "title" should be the easiest to try first:
Thanks. Struggling with it, but I'll keep at it. Will title really work if I am referencing a call to comment text? I'm going to give the :hover route a shot. Not too worried about style though. :)
Ellipsize will definitely come in handy. Thanks for the tip.