Here is an idea that wouldn’t be worth the time to construct lol

Open the movie with a younger Richard E. Grant hunkered down as he is in his hologram scene with Palaptine in TROS.

I would use someone who could do an impression of him,deage Richard e grant and give him the badges of a high level imperial officer (I’m trash with rankings lol)

Have Palpatine tell him to arrange everything for Exegol. The time has come.

All of this takes place on the bridge of a star destroyer. It would take place just before Vader and Luke meet the Emperor.

It’s too much work to carry out but I picture the star destroyer going through hyperspace.

It arrives above Exegol, and an officer asks Richard e grant “what now, sir?”.
Richard e grant would reply “we wait…”

And from there it cuts into the movie as we know it.