Mazda3Club.com : The Original Mazda3 Forum - Problems with Removing Downstream O2 Sensor

My '08 Mazda3 hatch recently threw a code (P0138) indicating that bank 1 sensor 2 is malfunctioning by reading a higher than normal output voltage signal, so I've been attempting to remove it for bench testing and possible replacement. The issue is that it's located in a very inconvenient location and also seems to be torqued surprisingly tight. I currently have the car sitting on jacks, and no matter whether I try removing it from the top of the engine bay or through the bottom of the vehicle, I just can't generate enough leverage to properly break it loose.

My question to those of you who've replaced the downstream O2 sensor on your vehicle is, how did you manage to remove it?

In attempting to work it loose, here's what I've tried so far:

heating it with a heat gun for periods of 5-10 minutes, then soaking in PB Blaster...to no avail, it still refused to budge.
heating it with a MAPP gas torch for 10-30 second intervals, then soaking in PB Blaster...to no avail, it still refused to budge.
turning the car on and letting it run for 10-20 minutes, then soaking in PB...to no avail, it still didn't budge when I tried removing the sensor.

I'm at a loss for what to do here. I barely have room to generate enough leverage to break this thing loose, and I can't tell if it's just torqued way too tight, or if I need to have the car on a lift so I can ratchet it off easier. This seems so simple to do, and yet I've taken over a week to do the above with no results.

Thoughts and opinions?