I'm assuming that with something like Revisited or something as radical, the editor would be rotoing Obi out from the background anyway and inserting a new one, so I didn't mean the scene was unsuitable - only that it would have to be altered :)

I have no idea if such a manipulation of Qui Gon would even be possible anyway. You'd have to have Liam Neeson saying the words for at least some of it. You could probably get away with a lot via cutaways and by having him more like Obi's ghost on HOTH rather than his walking around clear as day ROTJ version. Maybe have him in a misty, foggy setting like Dagobah.

The other alternative is to make Qui Gon a disembodied voice instead. Obi spoke to Luke in this way before. The key is to have more of the film with Obi wan, and even if Obi himself isn't actually speaking any more than before, scenes with him consulting his dead mentor help to push Obi to the foreground - more like the main character he should be than supporting cast to Anakin.