This code will do what you want but it assumes yoru taxonomy and post type have no heirarchy, e.g. your taxonomy works like tags not categories, and your post type cannot have parent and child posts.
This code belongs in a plugin or the functions.php of your theme:
function custom_rewrite( $wp_rewrite ) {
$feed_rules = array(
'reviews/(.+)/(.+)' => 'index.php?post_type=reviews&taxonomy_name=".$wp_rewrite->preg_index(1)."&post_name=" . $wp_rewrite->preg_index(2)
);
$wp_rewrite->rules = $feed_rules + $wp_rewrite->rules;
}
// refresh/flush permalinks in the dashboard if this is changed in any way
add_filter( "generate_rewrite_rules', 'custom_rewrite' );
Once the code has been inserted, go to the permalinks settings page and re-save to flush the old permalink rules and generate the new ones.
If your taxonomy or your post type IS heirarchical however, it can still be done, but you will need to modify the regular expression in the code accordingly. I am not familiar enough with regex to advise how.