Can custom fields be added without a meta box?

Add this code in functions.php

add_action('admin_init', 'wpse_87339_admin_init');
function wpse_87339_admin_init() {
    wp_enqueue_script('wpse_87339_admin', get_stylesheet_directory_uri() . '/js/admin.js', array('jquery'));
}

and create new js file name admin.js and then add the below code in it

jQuery(document).ready(function($) {
    // Remove all .postbox classes from sidebar
    $('#side-sortables .postbox').removeClass('postbox');

    // Remove .postbox from specific metabox (page attributes)
    $('#pageparentdiv').removeClass('postbox');
});