Rip out the Main Board, or replace the EEPROM..
Some EEPROM's are re-programmable but this is very rare especially in new phones, by definition eep'ROM' (Read Only Memory) means once its written, it can't be re-written.
Of course, as above.. not something usually done in legitimate circles.
One trick I heard used to work is to find someone having the same problem abroad e.g. US or Aus etc.. since their IMEI's are not tracked internationally and swap phones.. get eBay'ing (although again, advertising such a thing on eBay would probably be in breach of contract too!!)