You definitely want the one form to POST to /roles and the other to POST to /rights, but I'm not sure how that precludes you from using form_for.
Perhaps you haven't noticed that a form_for uses a block that has a do and an end? So you just create the first form with form_for do ... end and then create the next form with form_for do ... end.
You can have as many forms as you like on a single page.
Ciao, Sheldon.