I used a small piece of old breather pipe wedged in the corner to keep the flap lifted in the upright position, been there for 10'000miles +.
I've seen people drive a self-tapping screw through the side of the intercooler aswell to keep the flap held upright.
I've never had any trouble in the cold weather with it. The main reason for doing it is when your running high boost you don't want the flap to be pushed into the down position.