I don't think its doable at all. I think the best you can do is create a sort of muddled story where you don't really know whats going on. If we know the names Skywalker for Anakin and Luke and if we know that Padme is pregnant, then I think most people wont buy what Obi-Wan is selling to Luke for a minute. But I am in favor of someone trying it. Its enough of a debate to make it worth trying to see what its like. I just don't think theres enough material for it.

I'll tell you guys something else that isn't going to be popular. I think Lucas skated pretty on some pretty thin ice when he pulled the I am your father bit to begin with. I know a few people who were adults when Empire came out and several have said that I am your father was met with a fair bit of criticism. "Its like a soap opera" was the "its a bunch of muppets" complaint.

I'd be willing to bet that whatever you put together toward preserving that surprise will only worsen that possibility. Id guess thats probably part of why Lucas didn't worry about it.

From a cinema history perspective, "I am your father" is great. As an actual cinematic device. Its a little gimmicky.