My Black & Decker 3/8" drive battery powered impact wrench has a variable-speed trigger that allows me to do the same kind of thing. Hold firm pressure against the screw head after soaking the stubborn screw with KROIL for a while, and gently hammer on it in both directions. It's a lot simpler than hooking up an air line, firing up the compressor, etc.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!