Well in P3d you can spawn as human and walk about, you just cant interact ie enter exit vehicles. So Id have to say that it should be possible if you made the ‘human’ a vehicle selectable from the aircraft menu.
If this would of been my project (msfs) the 1st thing I would of done is modeled the world and then added planes, trains, and automobiles in as modules, but it seems they’ve followed in the footsteps of previous incarnations of the game.