Actually there would be a possibility. I don't know how feasible it would be for you but it seems that you could modify a portion of my setup to make it work. I have a full-fledged network at home and play GC on two different machines but I only have to update it on any one machine. The game files themselves are installed to a shared folder on the domain controller which is mapped to a drive (S:).
Here is the part that might work for you with some modifications: I use a public domain logon scripting language (Kix) to grab all the stardock entries and export them to a registry file on the server upon logout. When anyone logs in to any computer, it grabs the registry file and loads it. This ensures that both computers always reflect the same versions of updates and patches in the registry - otherwise the files and registry keys would be out of sync.
It seems to me that you could use a similar method of running a logon/logoff script (if you have XP or 2k) and extract the keys and contents of the following keys (if you have drengin.net or the appropriate keys if you have just GalCiv:
HKEY_LOCAL_MACHINE\SOFTWARE\Stardock\Drengin.net\Manager\Games\GC1
HKEY_LOCAL_MACHINE\SOFTWARE\Stardock\Drengin.net\Player
I am assuming that there is some cross-check and calculation built into game submission from these fields.
Then register your wife and extract her info to a separate file. Load the appropriate file upon login.
DISCLAIMER:
Now, not having tested this with multiple users and different serial numbers, I would strongly suggest that you: A) Back EVERYTHING up (including the full registry tree for StarDock);

Get some input from StarDock support as there is a possiblity that some key information is encoded in the file tree itself.
There are some other parts to this but they shouldn't really matter to you (like locking the registry file on the server when doing an update, running a separate script to force a writeout of the registry file upon update, etc...).