WooCommerce product permalinks

Add a filter for post_type_link, and change its value in a callback function.

Sample code, not tested:

add_filter( 'post_type_link', 'simple_woo_urls', 10, 2 );

function simple_woo_urls( $url, $post )
{
    if ( 'product' === $post->post_type )
        return home_url( $post->post_name );

    return $url;
}