How set defaults on wpLink()

Also an small example for change the url in link-button to use the url from installed blog. Use print JS in footer, not an include from js file via wp_enqueue_script() – ist faster vor development, specially for this small requirement, but not so on standard and fine, how the example from the other answer.

<?php
/**
 * Plugin Name: Change URL in Link Popup
 * Plugin URI:  http://bueltge.de/
 * Description: Adds a domain link button to the post editing screen.
 * Version:     0.0.1
 * Author:      Frank B&uuml;ltge
 */

if ( ! function_exists( 'fb_add_quicktag_button' ) ) {

    function fb_add_quicktag_button() {
        ?>
        <script type="text/javascript">
            // change link on Link popup in TinyMCE and quicktag popup
            ( function( $ ) {

                if ( typeof wpLink == 'undefined' )
                    return;

                wpLink.setDefaultValues = function () { 
                    $('#url-field').val('<?php echo home_url( "https://wordpress.stackexchange.com/" ); ?>');
                };
            } )( jQuery );
        </script>
        <?php
    }
    add_action( 'admin_footer-post-new.php', 'fb_add_quicktag_button', 9999 );
    add_action( 'admin_footer-post.php',     'fb_add_quicktag_button', 9999 );

}