How hard would it be to procure the rights?

Many things would have to happen to make it possible:

- SpaceX would have to want to sell the ad space.

- If NASA is paying for the mission, they may want to have a word (most likely "no").

- The owners of the Pan-Am brand would probably appreciate the gift, but I'd like to make sure they won't get mad before any such stunt.

- The Arthur C. Clarke and Stanley Kubrick estates would also have something to say, after all, this is more or less a reference to 2001.

I'm kind of surprised that SpaceX didn't consider that for the outside of the dragon capsule.

Note that the capsule has a camera inside of it (there are pictures from it on SpaceX's site) so when the hatch opens you can see pictures directly from a video camera that isn't under NASA's control.