He shows up as Victor, telling Logan he is his brother, Logan does not believe him, they fight etc, Logan gets the better of him , nearly kills him.
Someone from the government gets ahold of Creed, and tells him they have a way of giving him the power to defeat Logan without having to fill him with adamantium.
Cut to the end of the movie(a scene not unlike Anakin's transformation into Vader at the end of Sith)..Creed goes through the experimental procedure, he comes out looking just like Tyler Mane did in X-Men, larger, stronger, big black eyes...and like Logan, he has also had his memory wiped during the procedure. He is given the code name 'Sabretooth' for the first time.
So when he runs into Logan in X-Men, he is physcially transformed beyond recognition, has a new name, Logan does not recognise him as the guy who claimed to be his brother...and Sabretooth only has a fleeting memory that passes by him when he grabs Logan's dogtags...just as Logan did when he encountered Stryker.
Will they do it that way? Probably not, we probably won't get anymore Creed in the Wolverine movies, but he was teh best part of XMOW, so who knows, maybe they will go that way.