Rails 3 - Devise : How to skip the 'current_password' when editing a registration?

I've implemented omniauth with my devise model, so I can authenticate using other services. Password is not necessary anymore for my model, as users can authenticate using twitter, facebook...

Everything is working fine, but, when an user try to edit its registration, devise skip the process because the user did not inform the 'current_password' (which doesnt exist in some cases now).

I created a registration controller to overwrite the devises one:

class RegistrationsController < Devise::RegistrationsController
  def update
    super
  end
end

But I haven't find any documentation about how to skip the password verification, how could I do it in my update action?