Cache Response Headers in Dispatcher?

Hi,

I noticed in the following link:  http://dev.day.com/docs/en/cq/current/deploying/dispatcher.html

"Due to this, the Dispatcher stores only the HTML code of the page - it does not store the HTTP headers. This can be an issue if you use different encodings within your website, as these may get lost."

I created a JSON renderer, which sets the content type in the header to be JSON:

response.addHeader("Content-Type", "application/json");

This works the first time (before caching)

However, once cached by the dispatcher, the server sets the content type as "application/x-javascript"

I am guessing there is no way to override this.  Any ideas?

Thanks