It’s a combination of stuff we’ve talked about here, and stuff I read over at TF.net.
We all know it’s pretty much impossible to insert a scene where Vader lands on Courascant (spelling?) and finds out about Luke. But what if it happened on his TIE?
Vader could hack onto the rebels radio wave (or whatever you’d call it) listening to some (if not all) of what they are saying during the battle. This could explain that little thing he’s always twisting around. (What-the-crap is that? A thermos?)
We could rerecord one of the other rebels’ lines of dialogue using the name “Skywalker” (instead of just “Luke”). Vader could hear the name and maybe repeat it: “Skywalkah!” as JEJ says it so beautifully!

But then, of course, Han shows up and there’s no time to do anything.
But if you don’t like that, we could have it happen after the death star going boom. Instead of rebels, we could have an imperial officer contact Vader with the name of Skywalker.
The officer could say something like: “blah, blah, blah, SKYWALKER…I will transfer the data to you and the emperor immediately…”
Vader interrupts and says: “No *couch* I’ll, uh, tell the emperor myself.”
Officer: ”As you wish, Lord Vader.”
This would explain why Vader seems to be hiding this from the emperor in ESB.
Now, just using existing Vader footage, reverse, slowdown, and/or rework it. If you need longer shots of Vader (because his inserts are pretty quick) you could find someone with the latest version of adobe after effects. In the new version, you can slow any piece of footage down significantly without it looking like it.
For those who wanna peak at it: http://www.adobe.com/products/aftereffects/newfeatures.html
Then go to: See it in action, then click Timewarp.
It’s amazing! I wish I had the money for this!
Thoughts anyone?