You won't be able to eliminate the factory wideband at all. You may be able to do it if you are running an elaborate standalone.
For tuning, you don't want to measure preturbo a/f, best location would be inches behind the exhaust housing of the snail. Hell, even if you could get and accuracte auxilary a/f reading before the turbo, you'd get tired of replacing $100 burnt out bosch senders.
You can however eliminate the rear 02 and run a wideband there, I did that for a while in the winter when it was too cold to mess with removing my downpipe and welding a bung.