Hey, not so fast there - I ain't caved in yet!
Lifting, sure, forces applied anywhere can be resolved into a force through and a moment about the CofG - happy with that, but isn't a consideration of forces on the helicopter via their size, direction and direct point of application also a legitimate way to go?
Granted, the balloon and spring balance idea wasn't kosher - now, if the bikini girl was in the balloon basket with a little fan to provide the side force, that'd be different, but that's probably taking it a bit far... or perhaps she could be nude?? Now we're talkin'!
Seriously though, let me get this straight about your feather pen scenario - wouldn't the force of the fan act at the centre of pressure, surely over towards the feathery end? And if so, wouldn't that be resolved into a translating force at the CofG plus a moment around it, causing it to turn as well as move away?
If your aim was to get gravity out of the picture, isn't what you said like having a long regular metal beam, say, floating steady in space, putting a small rocket motor on one end of it at right angles to the long axis and firing it? Would you get a simple translation opposite the direction of rocket thrust, or would it turn as well because of the moment around the CofG?