When Vader kills Obi-Wan, perhaps he could have some trouble? What I have in mind is that Vader would swing his sabre at Obi, Luke would yell "Nooo-" and have it cut short, since Obi-Wan would still be standing. Vader could swear (bleeped out of course), and try again, repeating the same thing with Luke, Vader, and Obi-Wan as many times as it needs to become funny and as few times as takes to remain funny.

Oh wait...that wouldn't work if they were leaving the Death Star without him.

It could still be done though. Perhaps when they come of the ship, use that scene and have Vader suddenly fighting Obi-Wan outside, but have him fail to kill him. Then cut to a sped up shot of Obi-Wan going through the halls, implying that he is using force speed. Cut back to Vader, showing the doors closing, and have Obi-Wan and the team meet up in the control room thing, or have Obi go straight to the tractor beam thing and begin the scene in the control room thing beginning after Obi-Wan leaves.

I haven't seen ANH in a while, so I'm not sure how plausible this is, but I'm sure some of this could be used...if it's funny enough, that is.