1. Install your preferred keyboards from Market
2. Use ES file explore (with Root feature and RW mount enabled in the advanced setting) or use Root Explorer to copy the keyboard .apk file from /data/app to /system/app
3. Reboot and select the keyboard by pressing and holding at any text input box.
4. (optional) Sideload and install "Nookcolor Tools" from http://forum.xda-developers.com/showthread.php?t=868366. You will have an option to set keyboards.
So far this method does not work with
- Thumb keyboard (thanks fr4nk1yn)