AEM's installation instructions say to keep the sensor 36" away from the exhaust port on turbocharged applications, so the sensor won't burn up so quick. I figured that if the stock rear o2 location was good enough for subaru, it was good enough for me. So I took off my downpipe and drilled a hole just a couple inches away from the rear o2 sensor, then welded the bung there and mounted it up. Then I ran the cable from the thing through the grommet right in front of the clutch pedal. I guess maybe 02s and 04s are different, but I've never had an easier WB install than on this car. Get some zip ties to secure the sheathing underneath the car and you're good to go.
Run power from a 10a fuse, get a good ground, and you're golden.