PSU post_type_filter

update-permalinks.php

<?php	
	add_filter('post_type_link', 'force_isle_category', 10, 2);

	function force_isle_category($url, $post) {
		$top_cat = null;
		if ( class_exists( 'PSU' ) ){
		    if ( 'product' == get_post_type( $post ) ) {
				$product_cats = get_the_terms( $post->ID, 'product_cat' );
				foreach ($product_cats as $pc) {
					if($pc->parent == 0){
						$top_cat = $pc;
						break;
					}
				}
			}
		}

		// if top level cat and is product append it to the permalink
		if( $top_cat ) {
			return '/'.$top_cat->slug.'/'.$post->post_name;
		} else {
			return $url;
		}
	}
?>