Wish I could help. I just ran into the same problem. I’ll be looking in to adding this function, but certainly hope someone comes along with answers! Good luck!
Try adding this code to your template where you want your menu appear:
<?php wp_nav_menu( array( ‘theme_location’ => ‘primary-menu’, ‘menu_class’ => ‘topnav’, ‘fallback_cb’ => ‘topnav_fallback’) ); ?> then in Appearance-> Menu and create your new menu including categories, links and anything else.