foo.rb

# Is there a better way to achieve this without having to define #orig_foo in each subclass?
class A
  def orig_foo
    self.class.superclass == Object ? foo : method(:foo).super_method.call
  end

  def foo
    "foo"
  end
end

class B < A
  def foo
    "bar"
  end
end

A.new.foo #=> "foo"
B.new.foo #=> "bar"

A.new.orig_foo #=> "foo"
B.new.orig_foo #=> "foo"