You're not adding to the editor, I don't think, you're adding to the answer form. You have to edit the $form array. Something like this:
function form($form) {
if($form['title'] == qa_lang_html('question/your_answer_title')) {
$form['fields'][] = array(
'value' => 'your html',
'type' => 'static',
);
}
qa_html_theme_base::form($form);
}
Then you parse it on submit with qa_post_text('your_field_name');