Bongo Fury

I live in outer London and quite often drive my diesel Bongo inside the North and South Circular, where the ultra low emission zone will be extended next year. Does anyone know of a technical fix to get the Bongo to comply with Euro 6? Selective catalytic reduction would work but I gather has to be developed specifically for each application, so it wouldn't be an economic proposition for the SCRT specialists to do given the numbers involved.
I wondered if any more recent Mazda engine, petrol or diesel, could be installed as a replacement for the existing engine and would fit in the space and mate with the gearbox etc? (I assume not very likely)

Sorry can't help you on that but if you do get it solved I'd love to hear from you as I also live on the outskirts and occasionally drift into the north and south circulars. I do have another car I can use if I absolutely have to but as far as I'm aware the older Bongo TDi will not pass the ULEZ test in its current format, I'm not sure about the newest ones. I think it is really worth the discussion as I'm sure that London will only be the first with all the other big cities following suit especially now that London is becoming a ghost town apart from cyclists thanks to our wonderful mayor.

As I understand it no Bongo will pass the ULEZ criteria no matter what engine My son currently lives in Kew just inside the ring road so looked quite carefully at other than parking on the outer side of the ring road which is about to become controlled parking as well there is no way around the rules.