最好的解决方案是允许用户在添加/编辑页面时选择导航菜单位置。使用带有下拉列表（select）的元框，选择所有可用位置，然后将所选位置保存在自定义字段中：

/**
 * Register the meta box.
 */
function wpse_183868_page_nav_menu_meta_box_register() {
    add_meta_box(
        \'wpse_183868_page_nav_menu\',
        \'Nav Menu\',
        \'wpse_183869_page_nav_menu_meta_box\',
        \'page\',
        \'side\'
    );
}

add_action( \'add_meta_boxes\', \'wpse_183868_page_nav_menu_meta_box_register\' );

/**
 * Display the meta box.
 */
function wpse_183869_page_nav_menu_meta_box( $post ) {
    $selected = get_post_meta( $post->ID, \'_page_nav_menu\', true );
    wp_nonce_field( \'save\', \'page_nav_menu_nonce\' );
    ?>

<select name="page_nav_menu">
    <?php foreach ( get_registered_nav_menus() as $name => $label ) : ?>
         <option value="<?php echo $name ?>"<?php selected( $name, $selected ) ?>><?php echo $label ?></option>
    <?php endforeach ?>
</select>

<?php
}

/**
 * Save the meta box data.
 */
function wpse_183869_page_nav_menu_save( $post_id ) {
    if ( ! isset( $_POST[\'page_nav_menu\'], $_POST[\'page_nav_menu_nonce\'] ) || ! wp_verify_nonce( $_POST[\'page_nav_menu_nonce\'], \'save\' ) )
        return;

    $nav_menus = get_registered_nav_menus();
    $nav_menu = $_POST[\'page_nav_menu\'];

    if ( isset( $nav_menus[ $nav_menu ] ) ) // Paranoid - check the submitted value is definitely valid
        update_post_meta( $post_id, \'_page_nav_menu\', $nav_menu );
}

add_action( \'save_post\', \'wpse_183869_page_nav_menu_save\' );

if ( ! $page_nav_menu = get_post_meta( get_the_ID(), \'_page_nav_menu\', true ) )
    $page_nav_menu = \'default_location\';

wp_nav_menu( array( \'theme_location\' => $page_nav_menu ) );