Puggo - Jar Jar's Yoda said:

the reveal is significant and is meant to be a surprise. That is why they must be seen in the order 4,5,6,1,2,3. And for that reason, there is no reason to hide the reveal in the prequels.

Furthermore, it would be impossible to hide the reveal... when Ben talks about Anakin being a good friend that he was tutoring, who ELSE could he be talking about? He also says that Vader helped the empire destroy the Jedi. In ep.3 we watch Anakin do all those things, and then become Vader. You'd have to ditch pretty much all of ep.3. Hmm, not a bad idea, now that I think of it.

This is why it is not possible at all to have the reveal and also have episodic order. You should be watching them in release order for a whole bunch of other reasons, of course, but if you are wanting to have the prequels seen first and then the reveal still a surprise...well, you must be counting on the audience being a bunch of retards.

One scenario someone once suggested at TFN was that Kenobi had two apprentices or something, one that was good and one that was bad, and Vader kills the good one, and so all along the audience thinks Luke is the surviving offspring of the good one and that is who Ben is talking about (i.e. he really was betrayed and murdered by Vader), until ESB throws a curve ball and we find out Ben was really lying the whole time. This is kinda neat, but highly convoluted, and it still doesn't address the other issues of release-versus-episodic order, and it doesn't really change the current situation since the prequels were not done like this.