You could do that with a custom posts_orderby
:
add_filter( 'posts_orderby', 'wpa58715_posts_orderby' );
function wpa58715_posts_orderby( $orderby_statement ) {
if ( is_post_type_archive( 'article' ) ) {
global $wpdb;
$orderby_statement = "FIELD($wpdb->posts.post_author, 42) DESC, $wpdb->posts.post_author";
return $orderby_statement;
}
}
Swap in your author ID for 42
.