ActiveModelSerializerのこう書きたい

after.rb

class HogeSerializer < ActiveModel::Serializer
  attributes :id, :hogehoge
  has_many :fugas do |fuga|
    fuga.attributes :id, :fugafuga
    fuga.has_many :bars do |bar|
      bar.attributes :id, :barbar
    end
  end
end

before.rb

class HogeSerializer < ActiveModel::Serializer
  attributes :id, :hogehoge
  has_many :fugas

  class FugaSerializer < ActiveModel::Serializer
    attributes :id, :fugafuga
    has_many :bars

    class BarSerializer < ActiveModel::Serializer
      attributes :id, :barbar
    end
  end
end