Steam – How to shift game which is getting download to another system in Steam

As several people have mentioned, it is now possible to be logged in on multiple computers at once. Only one computer can be playing a game at a time though. If you start a game while another computer is already in one, you will be notified and told that it will close the other game if you start.

I think the following is the correct way to currently do what I wanted:

1. Ensure that Steam thinks the game is not installed. Close Steam just to be sure.
2. Copy the game files to SteamApps\common\<game_name>, where <game_name> is to be found out via googling/equivalent. In my specific instance, this was Batman Arkham City GOTY.
3. Launch Steam and install the game. The installation will go through a "Discovering existing files for _" stage.
4. Watch and wait as it downloads only the missing parts.

I still have to download 9.8 GB though (instead of 17) in my specific case.