Embed form within a form
Nesting forms in other forms is not valid in html.
see this post 
html nesting forms in forms 

You can always try calling the form directly via the actual form function instead of via drupal_get_form since the function returns a valid array of form elements. 
you'll have to somehow compensate for the missing hook_form_alter and hook_form_FORM_ID_alter. 

Note I haven't actually tried this, so I'm not sure how it will react on the empty $form/$form_state params. 

That already gets you all the fields in a dynamic way. 
Perhaps you can build a similar work around calling the submit/validate handlers directly too.