I've posted a patch for #9932 ticket to allow polymorphic routes to resources and nested resources:
map.resources :posts, :polymorphic => [:events, :articles] do |posts| posts.resources :assets, :polymorphic => [:images, :movies] end
# In view edit_post_asset_path(:post_type => 'events', :post_id => 1, :asset_type => 'movies', :id => 2)
=> "/events/1/movies/2/edit"
Please spend a bit of time to take a look at this ticket http://dev.rubyonrails.org/ticket/9932#comment:3 if it makes sense.
