I'd have used a mixture of techniques.
One not having Anakin a main character (he could have been a major secondary character like Lando or Yoda) that way you don't have to focus on him all the time.
Bear in mind that Anakin is only referred to by his first name (in the OT) half way into ROTJ so if they avoided calling him Skywalker they could have called the fallen Jedi Anakin until they were blue in the face and still keep the surprise for ESB.
It would also have given the PT a chance to focus on a totally new set of characters we don't know the fate of in the OT which would ramp up the drama as even people who had already seen the OT wouldn't know were the story was going with them.
Another would be obscuration, have several other possible Vader candidates including one that fits Obi-Wan description in ANH (a former pupil of Obi-Wan who becomes a Jedi and looks like he could turn on them all at some point).
Providing a more open ended 'death' scene for Anakin would have helped too.
I'd also would have had Yoda mentioned with awe but never seen so when he appears in ESB as a funny little gnome he is a surprise.