Partial, code snippet for the tutorial: http://www.vijayan.in/woocommerce-custom-product-sorting

custom_ordering.php

<?php
    /**
     * Callback method to implement A-Z & Z-A sort functionality
     * 
     * @since 1.0
     */
    public function custom_woocommerce_get_catalog_ordering_args( $args ) {
        $orderby_value = isset( $_GET['orderby'] ) ? 
                wc_clean( $_GET['orderby'] ) : 
                apply_filters( 'woocommerce_default_catalog_orderby', 
                    get_option( 'woocommerce_default_catalog_orderby' ));

        if ( 'reverse_list' == $orderby_value ) {
            $args['orderby'] = 'title';
            $args['order'] = 'desc';
        } else if ('alpha_list' == $orderby_value) {
            $args['orderby'] = 'title';
            $args['order'] = 'asc';
        }

        return $args;
    }