Instead of having you dig through that entire thread, what worked for me after trying out the different methods listed in the thread.
For stock root:
1. Get anycut from Market
2. Create a shortcut to accessibility and another for android keyboard debugging (the list might appear short, but you can scroll down)
3. Open keyboard debugging and check the box
4. Find the apk file you have for the keyboard(if you installed it from the market, move to system/app and another to your sd card or somewhere safe
5. Install the apk which is in system/app
6. Open accessibility, select the keyboard as input of choice (you might be getting force close errors by now, just keep closing them)
7. Go to the safe spot you saved the other copy of the apk file, install that, and then delete the one in system/app
8. Reboot and you should be good to go
Similiar idea, but instead of having to create shortcuts and you just copy the apk file to system/app and safe spot and then follow the instructions from step 5 and on.
Though I do find that on Cm7, it doesn't let me select the keyboard I want, so you might want to get anycut anyways, but for me, I use SlideIT and when i install it they gave me a little intro and it opened accessibility for me and I changed it from there.