Off the top of my head, I don't think adding it to q_list is the way to go; better to just add a div before the q_list; at the beginning of the q_list function, retrieve a single question from the database and output it as you want it to be displayed.
If you really want it in the q_list, this seems to work:
function q_list($q_list)
{
$postid = <yourpostid>;
require_once QA_INCLUDE_DIR.'qa-db-selects.php';
global $qa_login_userid, $qa_cookieid, $qa_request;
$post=qa_db_single_select(qa_db_full_post_selectspec(null,$postid));
$usershtml=qa_userids_handles_html(qa_any_get_userids_handles(array($post)));
$options=qa_post_html_defaults('Q');
$post = qa_any_to_q_html_fields($post, $qa_login_userid, $qa_cookieid, $usershtml, null, $options);
array_unshift($q_list['qs'], $post);
qa_html_theme_base::q_list($q_list);
}