OK, so somewhat long story.
My turbo bearings and seals died on my 2001 9-5 SE wagon about four months ago. After rebuilding the turbo with one of the Chinese kits for about $35 off ebay, the turbo works great. getting it off and back on were by far the worst part of the job. The turbo housing is built into the exhaust manifold. I was able to get the turbo out of the manifold leaving it attached to the head and keeping the exhaust system in place. But shortly after the turbo (within days) I started getting second O2 sensor codes and after replacing it with a new Bosch one, I started getting codes for a failing catalytic converter. My best guess is that the excess oil consumption (clouds of black smoke) from the bad turbo trashed the cat.
Not really wanting to spend the mega bucks for a catalytic converter for a 17 year old car with 160K miles I started messing around with alternatives. After looking at some electric circuits that supposedly make the ECU think the second O2 is getting good readings but not being able to get it to work I tried the extending the fitting trick to move the second O2 sensor out of the main exhaust stream.
So far after about a month and a couple of thousand miles, it looks to be working. I ended up getting a pack of two spark plug extenders and since the there is not room to put them in the fitting in the exhaust pipe and still get the O2 sensor in, I ended up welding them together at about a 45deg angle and using a very thin jam nut to keep the extension locked in place so the weight of the sensor would not unscrew it and let it hang down.
This effectively moved the O2 sensor about an inch farther out of the exhaust stream. The theory, is that the extra cavity between the main exhaust stream and the sensor is that it holds some exhaust and thus the sensor reacts slower to changes in the O2 level in the exhaust which mimics a functioning cat. It could be that my the cat slowly cleared itself from all the oil burning and it started working about the same time as I moved the sensor, but I doubt it.
For now I am calling it a success and I will pocket the money from buying a cat. (on the V6, both down pipes and the cat are one piece)

Obviously I can't recommend you do anything to bypass the emissions systems and if you live in a place that does emissions testing this will not work.

2001 9-5 SE wagon
2002 9-3 Viggen Coupe