gistfile1.rb

module B
  def self.included(base)
    class << base
      attr_accessor :catch
      def acts_as_catchall(hsh)
        @catch = hsh
      end

      def inherited(subclass)
        subclass.catch = subclass.superclass.catch
      end
    end
  end

  def method_missing(meth, *args)
    if s = self.class.catch[meth]
      return s
    else
      super
    end
  end
end

class A
  include B

  acts_as_catchall :cat => 'meow'
end

class C < A; end
class D < C; end

p A.new.cat
p C.new.cat
p D.new.cat

class X
  include B

  acts_as_catchall :dog => 'ribbit'
end

class Y < X; end

p X.new.dog
p Y.new.dog