Ha! Thats easy. Instead of having a single silencer sitting across the car, it'll have a small cat and a silencer attatched to each turbo outlet. That will get it through the annual test anyway and long jouneys with the missus. Will even fit the stock bumper holes. For trips to france and blats out in summer evenings it'll be no cats and no silencers just two straight pipes. Sounds bonkers but I doubt it'll be much more vocal than a fully decated OMG as the turbos muffle the noise a fair bit.