Playing someone who is over aggressive you are making some right moves by slwo playing big hands and let him come over the top of you. A couple of things that I like to do when going heads up depending on your chipstack is either
1.) All in with A-something it sounds crazy but it puts pressure on the other person.
2.) Just call or raise small with a big pocket pair allowing the over-aggresive player to come over the top of you and once he's commited the chips push him all in.

The most important thing in heads up though is chip stack which gives you leverage. If you have more chips than if he chooses to play the hand let him know that it will cost him the rest of his chips to play. In the end its whose more willing to gamble.

Thats just my style.