gistfile1.rb

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

      def catch
        @@catch
      end

      def acts_as_catchall(hsh)
        self.catch = hsh
      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

a = C.new
p a.cat