In config/routes.rb

  scope ":db" do
        resources :boxes
  end


From the logs:

Started GET "/multidb_two/boxes" for 127.0.0.1 at 2011-09-12 15:47:09 -0600
  Processing by BoxesController#index as HTML
  Parameters: {"db"=>"multidb_two"}
  Box Load (0.5ms)  SELECT `boxes`.* FROM `boxes`
Rendered boxes/index.html.erb within layouts/application (118.6ms)
Completed 500 Internal Server Error in 228ms

ActionView::Template::Error (No route matches {:action=>"show", :controller=>"boxes", :db=>#<Box id: 2, name: "bonjour", created_at: nil, updated_at: nil>}):