To me, this seems like a feature the app you're using with the GPX should add to its social settings with a Share With Friend(s) button. Specifically knowing that being in an environment where cell coverage might not be available, it can form adhoc wifi, and push across. Of course, they will want you to allow access to Contacts to know who your friends are. But you've probably already been requested for any of the permissions needed for this feature, because $REASONS