Very Easy From FlyInsideApp in the VR, click on SIM menu, and then on the bottom IMPORT WINDOW. The app will show you the list of your open apps, then select it and click Import.
If I fly with Flyinside for P3D, I can get pop-up windows (as defined in the aircraft's panel file) and live windows, e.g. Plan-G for navigation. I can't see how to do this in FFS - there is no Sim option to import a window, and I haven't seen any guidance on creating pop-ups in FFS, so I guess its not possible at the moment?