The way I'm handling Luke's "final attack" on Vader is fairly close to how it was done in the original, but the context of Vader's words have changed due to Leia no longer being Luke's twin:

Vader: "Yes, your feelings are strong for them. Especially for... Princess/Highness/etc." (I'm still working on the audio editing of this scene and haven't decided which lines sound the best)

Vader: "So... your feelings have now betrayed her, too. If you will not turn to the Dark Side, then perhaps she will."

So in the edit, Vader's not offering to tempt Luke's sister to the Dark Side, but rather the person he cares for the most (who's not related by blood).