Devils Advocate: I haven't been keeping up with this story but... Don't you only need the DPF for the NCT? After all these years taxiing, you must have a friendly mechanic who could take it out, blank off the error codes, and then re-install it just before the NCT. Rinse and repeat? If that's not acceptable, bit the bullet and get an EV. There's potentially €20k FREE cash there for the taking and you only have to keep the EV for 3 years.
Put your business hat on - your car is your money maker!