I've had this idea for a long time and you guys probably won't like it, but I will suggest it anyway.
To fix the issue of some of the sets of cloud city looking like they belong to the empire, lets actually have it be part of the empire!
The carbon freezing chamber looks like something the empire would have. Lets have the carbon freezing chamber aboard the Executioner instead of cloud city.
We'll just made a scene where we see the Executioner parked outside of cloud city. They aboard the ship and they have their little party there instead. We'll have to change some dialog around to make this work. The carbon freezing chamber is no longer experimental to humans (what the heck do they use that for anyways?), the empire uses it to torture people.
