BFTrick

<?php
// make the categories non hierarchical for their permalinks
function my_woocommerce_taxonomy_args_product_cat( $args ) {
	$args['rewrite']['hierarchical'] = false;
	return $args;
}
add_filter( 'woocommerce_taxonomy_args_product_cat', 'my_woocommerce_taxonomy_args_product_cat' );