I worked out a varient of the Fan-o-matic idea where Luke has been on Dagobah finishing his training (it's been agreed that Leia will wait for Luke before hatching the escape plan). After Yoda's death Luke returns to Tatooine to rescue Han only to find she has lost patience and has rushed off with Chewie to do it alone (leaving Threepio at Ben's Hut).

So the Trojan horse in Artoo is a rescue plan for a rescue plan buggered up by the Skywalker trait of impatiently trying to save a loved one.

In that set up Threepio's statement makes sense, Lando has been at the Palace for sometime and Chewie has left with Leia (shame he doesn't mention her).

http://originaltrilogy.com/forum/topic.cfm/ESB-and-ROTJ-Wishlist/post/357719/#post357719

I know Ady doesn't want to have Threepio in the first two prequels so perhaps some of his dialogue can be moved from there to cover his half of the conversation.