Alright, this starts with this simple warning:
You Could Break your device doing this!
DO NOT just try and flash the droid build, it won't work, and could break things.
This is the same with all android phones with custom builds.
Firstly, as I've mentioned before, this idea was first developed by Dext3r from the alldroid forums before they went down. Heavy credits to him!
Here's the basics of how this works,
1. copy mot_boot_mode to mot_boot_mode.bin
2. create a new mot_boot_mode as a script (like you guys already use)
3. the standard system boots and loads the moto init, which runs the mot_boot_mode which in turn;
creates a new ramdisk
moves some mounts and things
does a chroot to the new ramdisk
runs the init with the new init.rc
Using a Droid based CM build as a base you need to replace many lib's, binary files, and firmware files (for wireless etc)
Instead of doing a whole writeup on his process here's his post from his initial work, it needs to be adapted to work on the CM build, but it's pretty close.
Reboot to win
Dext3r was the first to do this, I can't stress that enough