Compress RailsBaseURI and controller into one path segment?

I would like to deploy a simple rest application via mod_passenger to a
sub-directory (RailsBaseURI) called /mailing_lists. The application
is very simple mand has a single top-level resource called mailing_lists and
sub-resources of subscribers:

  map.resources :mailing_lists, :path_prefix => nil do |mailing_lists|
          mailing_lists.resource :subscriber, :only => [ :create, :new ]

$ rake routes
new_mailing_list_subscriber GET /mailing_lists/:mailing_list_id/subscriber/new(.:format) {:controller=>"subscribers", :action=>"new"}
    mailing_list_subscriber POST /mailing_lists/:mailing_list_id/subscriber(.:format) {:controller=>"subscribers", :action=>"create"}
              mailing_lists GET /mailing_lists(.:format) {:controller=>"mailing_lists", :action=>"index"}
                            POST /mailing_lists(.:format) {:controller=>"mailing_lists", :action=>"create"}
           new_mailing_list GET /mailing_lists/new(.:format) {:controller=>"mailing_lists", :action=>"new"}
          edit_mailing_list GET /mailing_lists/:id/edit(.:format) {:controller=>"mailing_lists", :action=>"edit"}
               mailing_list GET /mailing_lists/:id(.:format) {:controller=>"mailing_lists", :action=>"show"}
                            PUT /mailing_lists/:id(.:format) {:controller=>"mailing_lists", :action=>"update"}
                            DELETE /mailing_lists/:id(.:format) {:controller=>"mailing_lists", :action=>"destroy"}

This means the resulting URIs with the /mailing_lists path
segment duplicated like this:


but I would like really to compress the first two path elements for the base
uri and top-level controller into one. I tried :as => nil and :as => '' which
is respectively ignored generates paths that do not actually work.

Any ideas?