You could change Yoda’s dialogue in ESB:

“That boy was our only hope.”
“No…he will choose another.”

In this way, when Luke is hanging from Cloud City at the end of the film, he reaches out to Leia and thus ‘chooses’ her to be custodian of his destiny if he should fail.

Then the dialogue for ROTJ would need to change:

“Luke…there is another…” (Cut out the word Skywalker)

Then when Luke speaks with Obi-wan, remove references to Leia being his sister:

“You were our only hope.”
“Yoda spoke of another.”
“The other he spoke of is your twin…your sister in the Force.”
“Leia. Leia’s my sister.”
“Your insight serves you well. Bury your feelings deep down, Luke. They do you credit, but they could be made to serve the Emperor.”

I imagine Obi-wan is used to stretching language to convey a point, and him saying that Leia is akin to a sister to Luke is in keeping with this. Luke may or may not understand that Leia is not his literal sister, but the later scene with Luke telling Leia that she is his literal sister could remain, as Luke continuing Obi-wan’s mystical language or by simply misinterpreting the meaning. The later canonicity of Leia as Luke’s sister would make sense based on this, and feels in keeping with the mythological nature of Star Wars to have a spiritual character like Luke to treat the mysterious machinations of the Force as literally analogous to biological systems.

The change fixes the issue that Yoda both knows about Leia as Luke’s sister and is willing to let her die in ESB, and Obi-wan’s confusion as to whether there is one or two last hopes. With Luke racing off to face Vader unprepared, Yoda is saying that the Force will choose another champion, and Luke will be the instrument of this choice. It also makes clear that Vader could never have sensed Leia’s Force ability in ANH since she isn’t chosen until ESB. Finally and perhaps most importantly, it keeps the universe from shrinking to nothingness in ROTJ as this new hope could only be someone Luke knows.