How to Add Custom Properties?

Q. [Maxwell - Feb 14, 2008] In the Developers Support section it mentions that I can create variables based on classes provided using JavaScript. (See question below) Ideally I would like to add a property to the comment class (e.g. comment.rating) that i could use on both the comment and layout pages, but since I don't have access to the object constructor on the server, I am at a loss.