Automatic ext-root sdcard after very first boot only?

I wish to have this script in my imagebuilder firmware (with asterisk, etc).
Anyone have ideas? I think its must be detected sdcard at very first boot, extroot it, then copy system on it, reboot, install some packages from config file, configure it if needs. I think its not hard to do. Anyone? :wink:
ps: i think Its can be done as option in gl-config (by default must be off) or its can be even added to gl-menu - ask if sdcard detected if you wish to extroot it or not (after password setup, etc).
Maybe its possible to extract the automatic first boot extroot script from raspbery pi (in raspbian) and add it to gl firmwares too?

First, which model do you have? Mifi?

Why do you want to exroot in the first time? I suggest you do this:

First record all the steps to make exroot work and write a script to do exroot and install everything you need.
Then test that script from a firmware for the first time.
Next put the script in imagebuilder and modify /etc/rc.local to run it

Answer is Yes.