Rails: nesting includes for serialized_hash

Given this class:

class Template < ApplicationRecord
  has_many :frames, as: :parent, dependent: :destroy
  has_many :frame_variables, through: :frames
  ...
end

How can I nest the deeper includes in this method? I want :frame_variables to be nested beneath their respective :frame.

Right now, :frames works, but :frame_variables isn't nested beneath :frames, which is needed for this method to work properly.

def serializable_hash(options = {})
  result = super(include: { frames: { except: :id }, frame_variables: { except: :id } } )
  result.delete(:id)
  result.merge(options)
end

Any ideas? Thanks.