There's an Open-Source project for the app "Keyboard from Android 2.3" from the Market. I am unsure whether it is the actual Gingerbread keyboard or just a faithful recreation, but it may be your best bet at having direct access to the keyboard's resources to uncover where this setting may be:
https://github.com/g1011999/Gingerbread-Keyboard
You could also try contacting the author, he may have some idea that could help you identify this setting.