Ideally, this solution will be simple and self contained.
I wanted to pull this off without any locally hosted server-side scripts. But as I thought this through, it became apparent that I would need at least one php file to provide proxy and authentication functionality.
So I built a basic php file that would take the CSV that Google Docs spits out, and returns a JSON object. This solved the xhr problem and allowed me more options in addressing a strange limitation of the Google Docs publishing system.
I am willing to accept that this system may need one php file to make it work.
That being said, I stumbled apon this beauty while researching for this project.
By using a predefined URL with your spreadsheet's id and a few extra parameters, Google will return a json object wrapped in <script> tags. Wrapping the returned data gets us past the cross-domain issues. One of the extra parameters defines the callback function that you want called when the data is finished loading. This should be a great feature for read-only content.
I still need to determine how to handle authentication for read-write content situations.