Actually it would be rather cool to have Vader's breathing noise at the Separatists meeting and see a Vader like helmet, from behind only to have the wearer telescope upwards on very robotic legs.
One could speculate that by ANH his cyborg body would be sophisticated enough to look totally human.
As his dialogue would be brand new you could add a few gripes at the inconvenience of being a ten foot giant in a seven foot corridor :-D