put a cover over it, sheet metal screw it in. A piece of galvanize bigger than the duct and screw her in.
Mission accomplished, and it went just like you said. I cut a piece of galvanized to cover the hole, popped in four screws, and duct-taped the whole thing because ductape is righteous stuff.
If anybody ever gives you any crap about being a dog, you let me know.