Actually, it's possible to do this!
Thanks to the hints from these guys:
I'll preface that with saying that it's a little finnicky for Spellforce 2, though. With any non-standard resolution (i.e. if you modify the config.xml manually to use widescreen, etc.), you are likely to face a weird issue with the "hot button regions" of the game's interface being abnormally placed. For example, when you roll-over interface buttons, you may have to position the mouse slightly above where you normally would. This issue seems to be a "coordinates displacement" issue; the distance by which "the buttons are off kilter" seems to be related to the height of the frame in windowed mode.
That being said, if you are using a standard resolution that you selected from the drop-down menu within the game, this works pretty damn well!
Download 3D-Analyze v2.36 from ToMMTi Systems; it is an awesome tool:
Run 3D-Analyze and click the big "SELECT" button near the top-left of the application Window. Browse to your Spellforce 2 executable, which, by default, is located at:
C:\Program Files\Spellforce\Spellforce 2 Gold\spellforce2.exe
(of course, if you don't have SF2 GOLD, you would browse to the appropriate location instead)
Here's where the magic happens. In the "Performance" area of the 3D-Analyze options, tick-on "force windowed mode".
At this point, I'd recommend that you click "Save batch file!" at the bottom of the interface, which will allow you to launch Spellforce 2 in windowed mode without having to go through this process each time.
Final points of note: 1) the game will run a lot slower in windowed mode on the average system, 2) you may experience weird gamma issues (which can be corrected, either in your graphics driver software, or the game settings), 3) there is a weird problem with the keyboard ceasing to work in Spellforce 2. The only way to fix this seems to be to quit-out of the game. Unfortunately, the issue also seems to be related to "alt-tabbing". Windows key + R will also free up any "mouse lock" you experience.
Report back with success/failure rates...