Lambda sensors with twin zorsts

[The Black Flash]

I'm going to be running an alfa v6 in a dax rush - this means that I'll have twin sidepipes. Now on the donor car, the exhaust all goes down to a single pipe at the cat, and the lambda sensor lives there. The ecu is Bosch Motronic.
So with twin systems, it seems I have 3 choices:

- run with the sensor in just one pipe, and assume that the other bank of cylinders is behaving
roughly the same

- a sensor in each, though I don't know how/if this could be wired up

- leave it out and just run open loop.

Anyone have any experience of this? Option 1 is seeming the most sensible to me, but I thought I'd ask the oracles of PH.