function add_enrollment_dates( $user_id ) {

    $update_data = array();
    $student     = new LLMS_Student( $user_id );

    $membership_levels = get_posts(
        array(
            'post_type' => 'llms_membership',
            'nopaging'  => true,
            'fields'    => 'ids',
        )
    );

    foreach ( $membership_levels as $id ) {
        $update_data[ 'llms_enrolled_' . $id ] = $student->get_enrollment_date( $id );
    }

    wp_fusion()->user->push_user_meta( $user_id, $update_data );

}

add_action( 'wpf_batch_users_meta', 'add_enrollment_dates' );