It might take something heavier than putty--maybe a b-b or a small fishing weight? I'm not familiar with how big the Hawkeye is, or whether you can access the insides.
If everything else fails, you could cut a short piece of stretched sprue, drill a hole to fit it in the underside of the plane where it might not be too visible; then glue the sprue in place to brace the plane on its nose gear.
I did this with a tail-heavy B-24, using a straight pin. In the photo, you can just see it ahead of the ball turret. Even in this 1/72 kit, I couldn't seem to load it with enough weight to make it sit right.
Whatever you try, good luck with it.