The fuel tank will be where it always is. I don't understand your point, but judging from the subtext, I'm assuming you're suggesting it's dangerous.
I would honestly face the torch away from the tank and toward the nut. I'm not suggesting to cut the nut off with a cutting torch--just to heat up the nut to probably the heat that the exhaust already gets when the car is warmed up. But rather than have the whole exhaust hot, I would just heat the nut up.
If that's extremely dangerous, then my apologies.
I don't recall the exhaust shop removing my gas tank when welding in the custom catback on my other car, and that was blasted with a mig