Hi I have the following route:

```
mount Spree::Core::Engine, :at => ':city_name/', :as => :spree

```

that produces urls like `/munich/path/in/engine` or `/new_york/path/in/engine`

How can I use an url helper to produce such an url, that modifies the city and uses an url helper of the engine? If the engine would provide an url helper for a product (e.g. `product_path(@product)`), is there something like

```
spree_path(:city_name => "munich").product_path(@product)

```

to produce an url like `/munich/products/1`?