if you get the car high enough, you can get to it from the bottom and inside the wheel. you do not have to take it off. also, the higher you can get the car the better because you need room to work around under there. the O2 removal tool is key, but if you have to, you can hack the heat shiled with a dremil tool and remove the shield, then the manifold and never mess with the O2. as a suggestion, hack the heat shield anyway so the next time you don't have to mess with the O2.
andif you are doing this on a sedan...be prepaird...the O2 socket is a very tight fit. you might be better off with buying a crows foot wrench of some kind that will fit the sensor.
and use lots of liquid wrench...it is your friend.