If all you want to do is temper it, an oven will work.
Are you suggesting this from your own actual experience?
What temperature is the fire achieving? How long do you need to keep it in there? How much protection does a thin layer of aluminium foil give to protect wood in a wood fire?
Its not what I would be advising you to do, that's for sure....
How would you recommend going about the tempering process? Would an oven work OK? Cheers.