I haven't posted here in a while, but I hit upon an idea that, like many postulated here, may or may not work.
Perhaps the "Luke and Leia" theme could play when Luke contacts Leia from under Cloud City, in place of the Force Theme. Of course, the original music could "bleed" through under the new music, so... I'm not altogether sure about this. It could work, but still...
Just thought I'd throw it out there.