alt3rn1ty: No, if you want Multi-player and uploading discoveries, you need the game to be installed via GOG Galaxy.
The game itself does not provide the communications necessary (pretty much the same if you bought the game via Steam, if Steam provided the game as an Offline Backup Installer and you could choose not to have Steam client itself installed, you would also not be able to play MP or upload discoveries).
For those of us who want just the Single player game, and dont wish to have any kind of client installed communicating with the outside world while you play, the Offline Backup Installers are just what the doctor ordered :)
So anyway to solve your connectivity :
1. Uninstall any GOG games which you have previously installed just using the Offline Backup Installers (if you have GOG games installed and then you install Galaxy, Galaxy will detect any GOG games already installed and thereafter will start updating them .. I believe this can in some unusual cases lead to a slightly confused installation, hence why you need to start afresh by installing Galaxy first, and then installing all your GOG games via Galaxy).
2. Install GOG Galaxy, give it your password for GOG access, and then go into its settings to get everything how you want it, and also give a path / Hard drive location where Galaxy will install all your games.
3. Install games via Galaxy.
Now every time you launch a game, Galaxy will be launched first and chain load the game, providing it with all the background resources needed for the Multi-player connectivity.
I will do as you suggest, I did so in the past but then I found it more practical to download a game version and then only the patches via offline installers. (The word offline should have rang bells for me...)
Do you think it's possible to backup special game versions via the Galaxy interface for future playing? With the offline installers I can do so by uninstalling and installing previous game version, NMS is the only game where I do this.