Carton/ Less Than Carton Pricing

I am looking for an extension that will allow me to have special pricing for items bought in multiples of 4.

Our product comes in cartons of 4, and we have a carton qty sell price, and a less than carton qty sell price. So if Mr. Customer buys 4, it's $15.00 each, if we have to break a carton, it would be $17.00 each.

Of course that is just an example, some cartons have a higher qty and cost more/less.

Does anyone know of an extension that will allow me to do this?

Perhaps this would help. Not sure, but maybe.
http://www.opencart.com/index.php?route ... on_id=4927