While writing out a more detailed description of the behavior, I stumbled upon the solution myself.
When you try to install the game over the internet, just let it start, and then cancel it. This will both remove the installation and download from the queue, but apparently also remove the knowledge of the installation from the Xbox One.
So:
- Start the online install
- Cancel it
- Return to the home screen
- Notice that the disc tile has now changed to "Install disc"
- Activate the disc tile to start the installation from the disc.
This worked, the game now installs from the disc. Obviously any downloaded DLC's will still need to be downloaded, but for the purpose of this question this is not relevant.
Now, what do you do when you get back home and want to plug in the external drive?
Here's what I did. I first uninstalled the game using the storage management.
This makes my Xbox One forget that I had the game installed. Make sure you don't delete any savegames you have on the console.
Then, you turn off the Xbox One, plug in the external drive, and turn it back on.
Once you do that, the disc tile still says "Install disc". Ignore that. Instead either use your pinned link to the game, the tile for the game (if it shows up on the home screen), or navigate to your games and apps list and activate it. You should get a message saying not to unplug the external drive, and that your game will be ready soon.
A few seconds later you can try again and the game should now start.
Can we do it at the same time? Ie. both fire up my accounts Battlefield 4 (he doesn't have BF4 on his account) and play it, together?
Yes, this is possible. I did it with Destiny, CoD Ghosts and some other games.
And your brother would also get xbox live gold access if you have it.
Is this illegal in any way?
Will there be any downsides to this? Such as both xboxes (which are now thus not our "home xbox" any more) require more frequent logins, or other such things?
I am using this for about one month and have no problems at all. As far as I know is this intended to used like this.
You just need to login once to setup the home xbox. After the home xbox is set your brother can login as usual.
Best Answer
While both users are signed in you have to be at the main menu, have the second player or guest player press the start button and that should load their user and after that you should be good to go to select campaign or versus and so on. If that don't work, after you already have both users signed in, quit the game and restart the game. This being a Xbox 360 game originally, you will need to press the start and options buttons on ones remote to set up said guest account on the Xbox one.