Nested resources: controllers and form input names

Let's say I have a model class like this

  class Parent < ActiveRecord::Base
    has_many :things
    has_one :special_thing, :classname => 'Thing', ...

and I want the associations to be handled by UserThingsController and
UserSpecialThingsController respectively. Theny, apparently, I have to
set up routes with explicit :controllers

  map.resources :parents do parent|
    parent.resources :things, :controller => :user_things
    parent.resource :special_thing, :controller => :user_special_things

Or is there a way to get this automatically?

As I want to edit the nested resources in-place on the same page as
their parent object, I have a view, that contains a forms like these

  <% form_for(@special_thing, :url => image_path) do |f| %>
    <%= f.text_field :name %>

  <% form_for(@things[0], :url => image_path) do |f| %>
    <%= f.text_field :name %>

The first thing to notice is that I have to give the :url argument, for
otherwise both forms would go to ThingsController instead of
the "nested" controllers.

Second, the element ids and names are unusable. What I get is

  <form action="/parent/1/special_thing"
    id="new_thing" method="post">
      type="text" />

Whereas what I need is, for the has_one case,

  <form action="/parent/1/special_thing"
    id="new_thing" method="post">
      type="text" />

and for the has_many case with the appropriate object ids used in

I just can't get this stuff to do (easily) what I think it ought to do.
That may well be an indication that I'm misunderstanding something
considerably. What's the right way?