You would need an engine management to be able to do it. I would just go ahead and put it right at 6" back from the turbo outlet and you should be fine. Your car is turbo in stock form right? Take a look at where the factory sensor was placed in the downpipe and that should give you the right idea of location.

I ran into a tuning issue with my car and with a friends with the o2 placement. I have been using my wideband that has a simulated narrowband output for the ECU. Since my wideband is 3 feet downstream of the turbo, I had to shift the reading outputs quite far for everything to line up perfectly. But if I were running a primary o2, I would have put it 6" behind the turbo (where the factory placement is).