the PT could have shown the careers of two jedis who are friends, their names would not have been revealed (you could make up an explanation that when you enter the official jedi orders you lose your name or something like that).
at the end one of them turns into a sith but it is not clear which one (this could be done by the bad jedi already wearing some kind of mask when he does the killings). in this way you would start the OT without knowing who Obi Wan and Darth Vader truly are. the fact that one of them had children would not be mentionned, maybe only a couple of scenes where one of them is shown flirting with a girl (Padme) could indicate in retrospect that this was Luke and Leia's mother. also, Yoda would not appear in this trilogy, so that his foolimg Luke on Dagobah still keeps its effect.
i came up with this in 5 minutes so i guess there can be continuity problems with it, but if developed more i think it could be made to fit with the OT.