Advanced Menu Question for link_after

if ( has_nav_menu( 'primary' ) ) {

			$args = array(
				'theme_location' => 'primary',
				'container' => '',
				'menu_class' => genesis_get_option('nav_superfish') ? 'nav superfish' : 'nav',
				'link_after' => '<span class="navpipe">|</span>',
				'echo' => 0
			);

			$nav = wp_nav_menu( $args );

		}

So as you can see I’ve added a pipe to the menu, unfortunately this is adding to the sub-menu items also. I know you can run conditionals inside an array but each attempt I’ve made has broken something. How would I say:
if top-level then add 'pipe' else ''
I do not want to remove the sub-menus I just do not want the sub-menus to have the link_after

Thanks in advance