AbleCommerce Shopping Cart Software

We are trying to add a coupon where a customer can purchase the first item at regular price, and receive a second at half off. That is simple enough. However, we have two 'styles' that we are offering this special on, and would like to to allow the customer to combine (buy product A at regular price, receive either product A or B at half off). Is there any way to do this? Or, can it be done by tweaking the code used for coupons?

Rick