Monroville said:

Another thought on the DS2: don't know if this could be done, but what about only showing the superstructured area (from Han and Co. arriving to when the rebel fleet arrives) to make it look like the Empire has a long way to go to finish it.

When the rebel fleet show up and the Emperor says "now witness the firepower of a fully functional battle station!", the DS2 spins around to reveal the central laser dish and that side being completely finished (to provide a "holy shit!" moment). Hell, even if you didn't alter the appearance of the DS2, that would be cool to see regardless.

But surely if they know that the DS2 exists and have its plans then there is a high probability they know how much of it has been constructed - even if they don't know it's working (as it is in the film already). I don't buy that they'd be that easily fooled - this is a 3D environment they're all flying around in. The DS2 would have to remain facing away from every rebel ship at every moment for such concealment to work. If the firing crater were hidden from the outside and made to look like the normal surface of the station that might work, but just to have it facing away isn't enough.