In my opinion, I think it would be much cleaner and more reliable to do this via FreeMarker (supported via the REST API) as opposed to trying to parse out information from the page. With FreeMarker, you can gather the exact pieces of data you need and format in the most appropriate form for your analysis.
I think the most common approach is to dynamically generate the web analytics code via FreeMarker, pulling in the exact information you need directly into the web analytics code. Another option to consider would be to build up a JavaScript object on the fly to store all the information for that page/request, and then reference that object in your analytics code.
