Adding fixed items to menu in template

Hi.
I’d like to hardcode a couple of fixed menu selections to the main menu in the Twentyeleven theme. They need to be inserted in the theme template file, so they are visible on all blogs created by users in a network blog setup, and can be changed/added/removed across the entire network by editing the header.php file. This means I can not use the menu editor in the control panel for this, cause that’ll just affect the current blog.

The standard main menu is called in header.php like this:
<?php wp_nav_menu( array( 'theme_location' => 'primary' )); ?>

I’d first of all like to add a feedback link like this one:
<a href="https://sitename.com/feedback" title="Gi feedback">Feedback</a>)

The thing is, if I just add this link below on the next line, it’ll not be shown in the main menu on the site. It’ll not even behave like a normal menu item with text and background colors inverted on mouseover.
So I need some assistance to get this link into the menu properly.