Some people over at the romraider forums have been busy reviving the open source tuning scene. Its now possible to read and flash pre-facelift gen 4 ECUs with the Nisprog tool, and also read and write the EEPROM that holds the immobiliser pairing data, all with a common $15 CH340-based VAG-COM cable. This means you can read the immob EEPROM data from your ECU, install a spare, flash your EEPROM data into the new ECU, and the car will start right up. Then you can flash the ECU happily without worrying about bricking the ECU. ECUs can be had cheap on ebay if you keep an eye out - I scored one for under $100
See the thread here and links therein:
https://www.romraider.com/forum/viewtop ... 40&t=19937
The below is confirmed working on my MY04 GT, and should work the H6 ECUs too:
Grab the compiled nisprog.exe and SH7055_35_EEPSCI4 kernel from the romraider thread (I may repost them here if there's any interest)
Pop them in a folder along with smprog.ini
Open cmd in above folder and run the following: (after hooking up the green test connectors near the ECU)
nisprog -f ssmprog.ini
spconn
setdev 7055
sprunkernel ssmk_SH7055_35_EEPSCI4.bin
The kernel will now be running in ECU ram
To dump the immob EEPROM (keep this somewhere safe - it's effectively your keys):
dm eepdump.bin 0 0x00 subeep
To dump your ECU ROM:
dm ecudump.bin 0 0
Flash ECU:
flrom myrom.bin
To flash the immob EEPROM data into a new ecu:
flsubeep myeep.bin 0 0x100
There are also CAN kernels with this functionally which should work on the post-FL CANBUS cars