delayable.rb

module Delayable
  def delay_instance_method(method_name, *args)
    Sidekiq::Client.enqueue DelayedInstanceMethodWorker, class.to_s, id, method_name.to_s, args
  end
end

delayed_instance_method_worker.rb

class DelayedInstanceMethodWorker
  include Sidekiq::Worker
  
  def perform(klass, record_id, method_name, args = [])
    if object = klass.constantize.find(record_id)
      object.send(method_name, *args)
    end
  end
end

widget.rb

class Widget < ActiveRecord::Base
  include Delayable

  # ...
  def foo
    delay_instance_method(:do_something_funky, 123)
  end
  
  def do_something_funky(bar)
  end
  # ...
end