Yeah its tough, I was going to say the story shouldnt contradict anything from the OT...
but saying that someone in the re-writes thread said what if Obi-Wan is Lukes real Dad, at first i kinda dissmissed it but if it could be done well and add a shock moment to the prequels (something that was a big thing for the OT) it could work out if written well...
anyway, dont give in! that leads to the darkside!