addind a default value to a restful route

map.resources :trackables
map.resources :activities, :controller => 'trackables'

I want my trackables_controller to handle activities request. The
above accomplishes the route, but does not allow for the
trackables_controller to distinguish between the type types of

Regular routes allow you to use tack on another value like:

map.connect "activities", :controller => 'trackables', :action =>
'index', :activity => true

which will allow you to reference params[:activity] in the

I have not found a way to do this with map.resources.