Wordpress : html code below content

i developed a plugin for WordPress. In this plugin i generate a html code and add this to the post. Have anybody a idea for adding generated HTML under the content/post field? now i generate the code and add this directly below the content with this method:

add_filter('the_content', array('xxx', 'custom_content_after_post'));

Here is a picture of my wanted plan:

via Chebli Mohamed