I borrowed a heat gun from a coworker. It had a locking trigger so I turned it on and set it down on top of the stove in the kitchen with the nozzle pointing into the kitchen. This left both hands free to handle the receiver and mag tube. I had a pair of heavy leather gloves to protect my hands. I kept turning the assembly so I evenly heated it. I periodically gave it a good twist with my hands. Once it reached the right temp, slight smell and wisp of smoke, it started turning. It did turn very slowly and I kept heating it a little as I turned it. No vise or strap wrench was necessary.
I also considered heating it in the oven. I think it would work well but I was concerned about chemical smells...mmmm...Loktite flavored cookies.