Best bet is to wait until they add it. I know it's on the short list, but ETA is unclear.
In other words: it's not possible jet.
You might use the old-school method (I'm not sure if it's possible in NXG). Before sub-panels, we used to simply build the screens next to each other. The next and previous buttons would then set the screen coordinates, and the next screen would magically appear. This will only solve the UI part, but won't do much for code separation...