Rendering directly from the controller into a named section of my layout

My layouts/application.rhtml contains:

   <%= yield :main %>

I would like to render directly from my controller into the :main
section - that is, without using the usual view incantation:

   % content_for (:main) do %>
      i am not crazy
   <% end %>

Instead, directly from my controller, I want to (essentially) do a

    render :text => "I am not crazy"

And have that go into the :main section of my layout file.