Radiant CMS: how to use form_for, fields_for inside radius tags

Question

I'm working on a bit of an extension for Radiant CMS that processes survey data. I'm trying to use form_for, fields_for and various helpers that rails provides inside pre-defined radius tags. These tags would generate the survey on Radiant pages.

Here's what I have in mind for integrating with Radiant:

<r:survey id="200">
  <r:survey:form>                 #<-- call to form_for
    <r:survey:questions:each>     # <-- calls fields_for
      <r:question>                # <-- renders question
      <r:answer_field>            #<-- renders input via text_field, text_area, etc
    </r:survey:questions:each>
  </r:survey:form>
</r:survey>

So when I call <r:survey:form>, it suppose to generate <form> tag. I can do it by manually crafting the html, but I'd like to use form_for helper and the like.

Is there any way I could achieve the following:

# ------ <r:survey:form> -----------------------------
  tag 'survey:form' do |tag|
    # call form_for which would render form header and open <form> tag
    tag.expand
    # form_for would end here, closes </form>
  end

# ------ <r:survey:questions>----------------------------
  tag 'survey:questions' do |tag|
    tag.expand
  end

# ------ <r:survey:questions:each>------------------------
  tag 'survey:questions:each' do |tag|
    result = []
    survey = tag.locals.survey
    # should call fields_for here
    survey.survey_questions.sort_by{|q| q.order}.each do |question|
      tag.locals.question = question
      result << tag.expand
    end
    # end of fields_for
    result
  end 

I hope that this explain what I'm trying to accomplish.