I used a kerosene heater in a pinch, just set the tire on top for a bit, worked well
Submerged tire and boiling water Sounds like a trip to the ER.
I fried a Burris on the propane grill; don't try it.
How about an electric fry pan with a tin house to hold the tire and heat in. Actually looking at my Weber charcol grill it should fit both.
Or a metal garbage can and heat gun / electric fry pan.
Boiling water sounds like a lot of work. All of the suggestions above will work. I use a garbage can quite often but found that my heat gun was too hot. Cheapo hair dryer works good. I have also put them in the cab of my truck on hot sunny days. Free and easy.
Torch
The metal trash can and heat gun sounds like an easy alternative!