Default [Q] Lost IMEI after flashing Cyanogenmod 11

Dear xda-developers users:

I have recently flashed the cyanogenmod 11 rom in my U8800 pro, following the instruction on this thread. (Installed TWRP and so on)

Everything worked perfectly, but in the process I lost my IMEI.

Sadly I have not a backup of my IMEI (I trusted the upgrade to go smoothly), but I have my IMEI number written down on the phone behind the battery. Is there a way to "reflash" my IMEI?

I found guides explaining how to do this, but all of them required to access some sort of service menu that is not avaliable on Cyanogenmod. Can you please explain me how to restore my phone to the original ROM (I have really no clue on how to do that!). Also a procedure to recover my IMEI without restoring the original ROM is appreciated.

Thanks in advance.