Or, is it possible to use a friend's PC in town that has broadband to download the updates in a way that I can take them to my home PCs and install them? It is even possible to get the updates unless you have an activated copy of GalCiv2 on your PC?
You can indeed, you just need to install SDC there and have a USB drive of at least 1GB (should fit DL and DA, but maybe not any modules) or a burner available; SDC can only archive the entire game, not just the updates.
1) Install SDC on an online machine (keep a copy of the SDC installer handy).
2) Log in on SDC, head to the Games section, right click on the game, and choose Archive Application->Download and Archive. If the game is already installed and updated on this machine you can choose Archive Application->Selected Application to pack it up without redownloading.
3) If the game has modules (GalCiv2 does, for example), you'll be prompted to archive them as well. If the media you'll use to transfer the game isn't large enough, you may need to decline and archive each module sparately; otherwise just say yes.
4) When the archive process finishes, you'll find the .sdc file(s) in C:\Program Files\Stardock\Stardock Central\BACKUP (this path is customizable in SDC's settings so it may vary). Copy the .sdc files along with the SDC installer to the portable media of your choice (CDR, DVDR, USB drive, etc).
5) On the offline computer, install SDC, then double-click the .sdc archive files in explorer to unpack them. That should do it, the offline machine is up to date.