If you have and Advance theme, you can overwrite the body function like this:
function body()
{
$this->output('<body');
$this->body_tags();
$this->output('>');
//The custom part starts here
$this->output("The code you want to write in here");
$this->body_script();
$this->body_header();
$this->body_content();
$this->body_footer();
$this->body_hidden();
$this->output('</body>');
}
if you don't have an advance theme you can change the qa-include/qa-theme-base.php, but if you upgrade, you will lose that part of the website.