rails3 app:
session_store.rb:
module ActionController
  module Flash
    module FlashHash < Hash
      def method_missing(m, *a, &b);end
    end
  end
end
SESSION_MEM=MemCache.new({
  …...
 :name_space=":session:#{your_name_space}"
})
YourApp::Application.config.session_store :mem_cache_store,:key => ,:domain=>,:secret =>,:cache => SESSION_MEM