Okay, here's my suggestion for the ROTJ-flashback. The shot-descriptions below are quite obviously the ones that accompany the previous line. They should probably have been above the lines rather than below, but hopefully you can imagine how it would come together.

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Luke: "Why didn't you tell me? You told me Vader betrayed and murdered my father."
Obi-Wan: "Your father..."

(At this point, the scene fades to white and switches to a flashback. The music used should probably either be "Anakin's Betrayal" or "Padme's Ruminations". The first shot we see is the close-up of Anakin with yellow eyes)

"... was seduced by the Dark Side of the Force. He ceased to be Anakin Skywalker and BECAME Darth Vader."

(Shot of Anakin burning)

"Anakin was a good friend."

(A shot of Anakin and Obi-Wan as friends, probably something from the beginning of ROTS.)

"When I first knew him, your father was already a great pilot."

(Anakin in the Naboo Starfighter in TPM.)

"But I was amazed how strongly the Force was with him. I took it upon myself to train him as a Jedi."

(Anakin and Obi-Wan at the celebration in TPM)

"I thought that I could instruct him just as well as Yoda. I was wrong."

(Anakin preparing to kill the younglings.)

"He's more machine now than man; twisted and evil."

(The shot of Anakin's cybernetic hand trying to climb up the volcano. The ominous image fades to white and we return to the movie.)

Luke: "There IS still good in him. I've felt it... I can't do it, Ben."

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And then the scene would go on as usual. Like I said earlier, I think a flashback here could be quite effective. And it wouldn't be very difficult to put together.