Maybe an idea could be to use google earth as an external viewer for FlightGear?
Here is discussed the script "
Xplage", which does a similar thing for "X-Plane": The flight simulator get's configured to spit out at a regulat interval the view position in space (location and orientation), and the script takes that data and transforms it into a KML-input for google earth, which in turn adjusts it's view to fit the flight simulator's view.
Of course that is not exactly the same as having a native flight simulation within google earth' scenery; not so smooth and when it comes to be close to objects maybe also offsets and differences (because OSM data is not the same as google's data), but it might help to explore more realistic geography and scenery with flight sim?
Could that be an idea?
I think in general it should be possible, to utilise FlightGear's I/O-mechanism to produce the necessary output and to write a script similar to "Xplage".