Single turbo on dual exhaust

Are you asking on dual turbos, or how to take a single turbo, and split it into dual exhaust?

If you are talking exhaust:
If you have a good dual system under there, I don't think it would be to bad to split it under the vehicle, (somewhere near trans tunnel?) to join the existing tubing.

If you are going to add exhaust afterwards, a sizeable single system will keep velocity, and you could probably go single in - dual out on the muffler, and have dual tailpipes run, if you are looking for the "dual exhaust" look on the back of the car.