Mk3 2zz swap O2 sensors

Hey all,
Im using a USDM 2000-2001 Celica ecu for my 2zz swap which requires one O2 sensor after the catalytic converter.
As far as I know, our Spyders didn't have a downstream O2 sensor (atleast mine doesnt) so I won't be able to run an O2 sensor after the cat.

My MWR header has two spots for O2 sensors on it but I suspect this will cause a CEL if I run both sensors to the header.
Has anyone found a solution for this or will I just need to drill a hole for the sensor after the cat? Or perhaps running both to the header will be fine?