Because the broken --parkpos option in FlightGear 2016.1.0 (current version in Git next) doesn't seem easy to fix (at least to me ), I have added a workaround in FFGo, currently only in the Git repository. In the Preferences dialog, Miscellaneaous tab, there is now a checkbox saying “Fake the --parkpos option”. If you enable this, then instead of passing for instance --parkpos=A10 to 'fgfs', FFGo will pass the --lat=..., --lon=... and --heading=... options corresponding to the parking position.
Note: after changing the option in the Preferences dialog, you have to open the parking popup once and select an item (a startup location or “None”) for the change to be effective. in other words, an already selected startup location keeps using the same mechanism (--parkpos or --lat/--lon/--heading) until an explicit choice---which may be the same---is made via the parking popup.
Hoping this will help a few in these hard times...
Edit: added the “Note:” paragraph.