Why do I think an impact wrench is a really bad idea?
Maybe there's an itsy bitsy one on the market but the common ones need a pretty good whack with a beaten' tool
My reaction as well.
Aeons ago, in a moment of desperation, I released a stuck screw from a dewar body by heating the dewar gently, to about 200F as I recall, and by keeping a chunk of dry ice in contact with the screw head. After an arbitrary interval - but one that seemed long enough for the screw head to have established a significantly different temperature than the dewar, if it was ever going to - an orbital sander was held in contact with the shaft of a screw driver that tightly fit the stuck screw's slot. With a lot of downward and rotational force applied, the screw came loose. Three sets of hands were involved: holding the dewar, holding the sander to the screwdriver shaft, and handling the screwdriver.
I'm not sure a camera body would withstand the same amount of downward pressure that the dewar did, but by coupling a heat differential and vibration, maybe something good will happen.
Acetone seems good to me too.
Good luck!