I had another idea spring to mind while showering (I have heard this is an amazing spot for inspirations, such as it is)

The Episode II flashback:

When Obi-Wan is on the ship, and he whispers Anakin’s name, and it cuts to him in the bacta tank, and the camera holds and slowly pulls away from him, HARD CUT to that flashback. And let the flashback run uninterrupted there (would need extensive sound effects re-working, obviously, as well as the deepfaking) but the major change here would be a scoring one: Set it to Anakin’s Theme. Maybe the concert arrangement, maybe a different performance of the concert arrangement, I don’t think it got used much in Episode I but I think the sort of wistful/forlorn mood of it would fit here decently - back-time it so that the big swell at the end of the piece that resolves into the last few notes of Imperial March comes JUST as Anakin knocks the saber out of Obi-Wan’s hand, so that the descending notes of the march are playing as Anakin smiles, and when that shot is at its end (hopefully, so that the final note of Anakin’s Theme is ringing out, hard cut to Vader getting his suit put on as the actual Imperial March plays. (maybe the intro/ostinato part over the suit up bits and the melody hits on the first real shot of him in the suit).

For a little extra zazz, maybe have the last 20 or so frames morph his eyes to sith/yellow, just long enough so you’re like “What the hell was that” before the cut to the next shot.

By cutting out the ending of the fight where Obi-Wan demoralizes him with another “humiliating” lesson, the flashback becomes Anakin’s completely, and more like a misremembered daydream version of that flashback. He’s lying to himself about how good he really was, and it also helps as motivation to make him feel like he could do that to Obi-Wan again if they ever meet up.

Also I feel like we never got an actual moment of Anakin’s Theme legitimately transforming into Vader’s, and this would be a pretty unique opportunity to do that.