Ember Routing with renderTemplate and setupController

I am building an Ember app to show a simple Twitter-like tagging system. When a user visits /items, he or she will see a list of all items. When the user visits /tags, the user will see a list of tags as links. When the user clicks one of these links, the user should be directed to /tags/:id and will see all items tagged with that specific tag. Then the user will be able to search/sort/manipulate the items as he/she would be able to from the ItemsRoute.

How can I make TagRoute use ItemsController and render the items template, using the tag's associated items as the model?

I have tried different combinations of the hooks in TagRoute, and I'm not able to find a recipe that works. There seems to be a fundamental misunderstanding on my part.

Here is my relevant code:

router.js.coffee

App.Router.map ()->
  @resource 'items'
  @resource 'tags', ->
    @resource 'tag', path: ':tag_id'

routes/tag.js.coffee

App.TagRoute = Ember.Route.extend
  model: (params)->
    @get('store').find 'tag', params.tag_id
  controllerName: 'items'
  setupController: (controller, model)->
    @controllerFor('items').set('model', model.items)
  renderTemplate: ->
    @render 'items', ->
      into: 'tags'
      controller: 'items'

templates/tags.hbs

<ul class="tag-list">
  {{#each tag in model}}
  <li>
    {{#link-to 'tag' tag}}
      {{tag.name}}
    {{/link-to}}
  </li>
  {{/each}}
</ul>

{{outlet}}

models/items.js.coffee

App.Item = DS.Model.extend(
  body:       DS.attr('string')
  checked:    DS.attr('boolean')
  tags:       DS.hasMany('tag')
)

models/tags.js.coffee

App.Tag = DS.Model.extend(
  name:             DS.attr('string')
  taggings_count:   DS.attr('number')
  items:            DS.hasMany('item')
)

Currently, this give me an error:

Error while processing route: tag Cannot assign to read only property 'name' of function () {
        return {
          into: 'tags',
          controller: 'items'
        };
      } TypeError: Cannot assign to read only property 'name' of function () {
        return {
          into: 'tags',
          controller: 'items'
        };
      }

Looking at the Ember Routes Inspector in Chrome, the controllerName property is the only one which overrides Ember's defaults, and Ember still tries to render a generated tag template.