If you are building this as a curbside and not worried about the underside of the hood, I would find some round sprue or styrene rod that is close to the same diameter as the hole and glue a small section of it into the hole. For cement, I would use tube glue. Put a good amount of glue around the rod and then insert it into the hole. The excess glue will ooze out and form a good seal around the rod. Once the glue has had ample time to dry, cut off the excess rod and sand the area smooth using various grades of sanding pads or sticks. I have used this technique several times in the past and have never had a problem with shrinkage around the repair, as you might have with some putties.