Read a copy ECUs EEPROM file (not the flash .bin), then use tunerpro to edit the file and update the SKC to match that of the cluster.
Then, use eeprom tool
http://nefariousmotorsports.com/forum/index.php?topic=6134.0to set the immo on and fix checksum. It might be possible to change the SKC via the EEPROM tool (instead of in tunerpro), I just dont remember if this feature is built in, likely so. Note that eeprom tool can be used as standalone command line program or it is even easier to use with the visual logger GUI.
Once you have the EEPROM file ready, then you will need to use a bench-flash cable to flash it directly back to the ECU in boot mode (not via the cars OBD port!).
With matching SKC in cluster and ECU, and with the immo turned on then you should be able to pair new keys to the IMMO.