Jetty supports the Servlet API feature of RequestDispatcher.include, so one URI/resource can be included in another page. The trick is how do you trigger than in the content that you are generating? >From the servlet, it should be easy enough to get a RequestDispatcher and call it directly. If you want to do this from static content, then you will need to use something like JSP to process that content and allow dynamic components to be added. For wordpress... either do it in wordpress... or do something very complex about intercepting responses and rewriting with the new content - possible but a lot of work.
