Coupon for a single (non-specific) item

Is there a way with OpenCart, or an extension, to allow a person to use a coupon on a single item? Not a specific item, just a single item. It could be a shirt, a hat, a pencil, whatever, we just need them to only be able to apply the coupon to an item (could default to the most expensive item in their cart).

I google-fu'd the mess out of this topic and couldn't find anything.

Thanks.