Rakefile

class Tricksy
  def self.lulz
    puts "denied"
  end

  def self.singleton_method_added(name)
    Object.const_set(:Tricksy, RealTricksy) if defined?(RealTricksy)
  end

  RealTricksy = self.clone
end

task :default do
  load "lib/tricksy.rb"
  Tricksy.lulz
  SuperTricksy.lulz
end

tricksy.rb

class Tricksy
  def self.lulz
    puts "lulz"
  end
end

class SuperTricksy
  def self.lulz
    puts "super lulz"
  end
end