I just thought i'd add my two cents. I honestly don't think that the Emperor/Vader scene from ESB should be in ANH. It just doesn't fit.
I think that Gorilla's ideas for the reworking of the dialogue when you get round to ESB is probably the best way to go.
BUT i do like the idea of the Imperial Officer hologram as Vader approachs Coruscant/Imperial navel base/somewhere (BUT NOT Executer!) and i agree with its possible placement between Luke arriving triumphant back on Yavin 4 and the medal ceremony if that works.
Now if you have the conversation with Vader telling the officer that he'll tell the Emperor about Skywalker, then maybe with the ESB scene you could go with Gorilla's ideas but maybe keep the new dialogue when the Emperor tells Vader its the offspring of Anakin Skywalker and Vader says "How is that possible?" and the Emperor Saying "search your feelings ...etc...He could destroy us". and then with those two pieces we will have to assume that Vader never did talk to the emperor about Luke. That he had a possible motive of finding Luke first without the Emperor's knowledge and bringing the Emperor down together.
I think that would make a great addition to the way Vader is thinking and his relationship with the Emperor at that point.
Now if that doesn't seem to make sense or sit very well with everyone, how bout still adding the Imp Officer and Vader as has been suggested in ANH with Vader offering to tell the Emperor himself, and then in ESB when you do it go with all Gorilla's dialogue changes, Vader doesn't ask how its possible he just goes "Yes master" like in the original. That way we get the impression that they both knew about Luke but maybe haven't really discussed it. And there we still get an undertone that Vader wanted to find Luke first before the Emperor got involved. Especially ,as been pointed out already, he uses Skywalkers name at the very beginning of ESB when he's sending the probes everywhere.
Just a suggestion and i know i haven't explained myself enough probably but i hope you get the idea.