This gist shows how to make a polymorphic association for users in rails which have an specific role, such as Member, Admin...works with devise

gistfile1.rb

##Userable
module Userable
  def self.included(base)
    base.has_one :user, :as => :userable, :dependent => :destroy, :autosave => true
    base.validate :user_must_be_valid
    base.alias_method_chain :user, :autobuild
    base.extend ClassMethods
    base.define_user_accessors
  end
  
  def user_with_autobuild
      user_without_autobuild || build_user
  end
  
  def method_missing(meth, *args, &blk)
      user.send(meth, *args, &blk)
    rescue NoMethodError
      super
  end
  
  protected
  
  def user_must_be_valid
      unless user.valid?
        user.errors.each do |attr, message|
          errors.add(attr, message)
      end
    end
  end
  
  module ClassMethods
    def define_user_accessors
      all_attributes = User.columns.map(&:name)
      all_attributes << "password"
      all_attributes << "password_confirmation"
      ignored_attributes = ["created_at", "updated_at", "userable_type", "encrypted_password", "id", "userable_id"]
      attributes_to_delegate = all_attributes - ignored_attributes
      attributes_to_delegate.each do |attrib|
        class_eval <<-RUBY
          def #{attrib}
            user.#{attrib}
          end
          
          def #{attrib}=(value)
            self.user.#{attrib} = value
          end
          
          def #{attrib}?
            self.user.#{attrib}?
          end
        RUBY
      end
    end
  end
end

##Act as user
class ActiveRecord::Base
  def self.acts_as_user
    include Userable
  end
end

##User model
belongs_to :userable, polymorphic: true

##Polymorphic model
acts_as_user

This was helpful.
What did you do for the signup, signin etc. ?? How do you configuring the routes for the models?

Thanks