It is possible to add to Disco. How difficult, I can't say as I don't know.
BTW Jinx, even though the majority of FL's bases and planets are one the single plane, that does not mean the game is not very 3D. Every system and process in FL is completely 3D. The systems are in fact large circles. Bases can be made to be up or down the Y plane as easily as changing one number in the system's .ini file. (pos = x, y, z) pos = 10800, 6000, 8000 would make a base that is 10,800 meters to the right of the center of the system (nav map shows the X and Z planes), and the 8000 would be 8,000 meters above the center of the system (center in relation to the nav map. In reality, it would be 8,000 meter behind the center of the system, if you were looking at the center from the center of the Y plane. The 10,800 would be to your right still. In this 3D view, the base would be 6,000 meters above you, and you'd be looking 'up' at it.
For example; Vespucci. Planet Guadamala is at 0 on the Y plane. La'paz Depot is somewhere between 1,000 and 3,000 on the Y place. This puts it ABOVE the planet.