Essentially snip out all the “Leia is my sister” bits in ROTJ and add the “There is another” line into that dream sequence in TFA and that’s pretty much all you can do to make that happen. A lot of effort for something small.
If Leia has real Jedi skills in Ep 8, this idea might not work as well.
Indeed, but Leia was established as being Force-sensitive in ESB, we can fiddle with what we get. The only bad thing is I really enjoy the Luke v. Vader duel in ROTJ, and Leia’s relationship plays a pivotal role in that.
There’s the argument that Luke is the only one using the Force when he contacts her on Bespin.
Also, I prefer the interpretation (originally proposed on Star Wars Minute) that Luke’s mind immediately jumped to Leia as ‘your sister’, but his real sister was someone entirely different. Ben, knowing that the only way his real sister would be safe is if she stayed anonymous, played along with Luke in case his thoughts later betrayed him. Lyin’ Ben strikes again!