I am searching for a solution. We would like to create private buy x, get y promotions triggered by a coupon code. When X is in the cart, and the coupon code is entered, Y should automatically be added to the cart. Or a spend X, get Y, where once you hit the threshold and enter the coupon code, Y is automatically into your cart.
Within shopify, you have to have the free gift in your cart for the code to work, and I haven't been able to find an app that does. All of the apps I have found automatically add the gift to your cart, which doesn't work for us because we want to segment offers.