Is it possible to have an automatic discount of $1 per extra item if purchasing 2 or more of the same item?

We would like to offer a discount on 2 or more of an identical item in a certain price class.

What we want to do is have a discount of $1 per extra item applied when the customer orders 2 or more of any item in a specified price class. We do not want it to apply if the customer orders 1 of one item in the price class and 1 of another, it has to be more of the same item.

Is this possible and if so, how would I go about setting it up?

I have set up a discount code for a price class where 2 or more of the item will trigger a discount of $1 but it only does it once.  We would want each additional item to trigger a $1 discount.

Thanks for any advice,

Phil