Routing issue

I have presently this in my routes.rb

map.resources :media_containers , :has_many=> [:media_items]

as the media_items can have 'libraries' and 'medias' inheritances
(STI)

rather than writing a route for a new media_item, with a parameter to
specify the type (elibrary or not) , like :

new_media_container_media_item_path(@media_container, :lib =>
"1") .. or :lib=> "0"
/media_container/media_container_id/media_items/new
:action => new, :controller => media_items

I would like to have an URL like this (hidding the /media_items)

new_media_container_elibrary_path(@media_container)
/media_container/media_container_id/new_library
:action => new_library, :controller => media_items (!!)
and
new_media_container_emedia_path(@media_container)
/media_container/media_container_id/new_media
:action => new_media :controller => media_items (!!)

is this possible ? how should I define it in my routes.rb ?

thanks fyh

erwin