As someone has already mentioned, the only way this could be fixed is by doing a radical edit of ANH (which I'm against as this would mean making the OT fit with the PT) or somehow giving Obi Wan another apprentice in the prequels - impossible.

Going back to my radical idea before (which was pretty much shot down by most people) the way to fix both in one fell swoop would be to not have Anakin appear in the prequels at all. Hayden is named something else. Let's just call him Puke Whinetalker. That way, in ANH, we think he is referring to Hayden's character when he says "a pupil of mine until he turned to evil" but then it turns out it's not that guy at all, and he was just saying it to spare Luke's feelings.

If Obi Wan never referred to Luke's father as "Anakin" in the hut scene in ANH, things would be a lot simpler. All that would need to be done is omit the name Skywalker from the prequels entirely. That way, we still have a hunch that Vader is Hayden, but no idea that he is Luke's father.