I agree with Joan,
It is best to wear an eye-patch and use a hook instead of your hand. And if you really want to refine your Chinese "r" it is necessary to grow a beard and get a wooden leg as well. You would really kick ass by also adding a side-kick parrot on your shoulder.
Haha, just joking Meir.
I've had some difficulties with the Chinese "r" as well but it's only a matter of listening to Chinese people speak and try to repeat their exact pronunciation. This might sound really easy, but for me it was the only way to master this "r". The thing that Sonnenblumen said about the usage of the tongue is absolutely right too.