I believe the trick the OP is thinking of is for removing a fixed wheel sprocket from a threaded hub.

Removing any threaded sprocket from a freewheel is impossible unless the freewheel is immobilized first. Otherwise it'll just spin backward with your torque applied to the sprocket.

If you want to remove the smallest sprocket without special tools, you can try this method that I would reserve for field emergencies. (two people required)

Shift to low, and brace the bike so it can't roll.
Set the crank horizontal, and have one person maintain steady pressure on the pedal.
stand behind the bike, and set a small punch on a near tangent against the smallest sprocket, and try to tap it loose.

WARNING -- while the method will usually work when done right, it's also a good way to brake a tooth off, so make sure the punch is pocketed as low against the tooth as possible, and don't pound away like a gorilla.