
After some work, I found the solution -- it requires editing a file within the CS2 (or CS3) application bundle. Full instructions can be found in this thread on Adobe's forums.
[robg adds: The linked thread has more detailed instructions and a screenshot. In case that ever goes away, however, here's the executive summary version:
- Quit CS2/CS3 if it's running.
- Control-click on CS2/CS3 in Finder and choose Show Package Contents from the pop-up menu.
- In the new window that opens, navigate to Contents.
- Make a backup of Info.plist
- Open Info.plist in your favorite pure text editor. Near the bottom, you'll find three instances of the super-long version string. Change the long string in all three lines to 9.0.2 (or 10.0 for CS3) and save the file.

