Question Excluding a .jar from the build

I'm using Unity's IAP plugin, but with a custom Amazon implementation that also includes Amazon's SDK. So I get the following error when building the apk:

Code (Boo):

1.   java.lang.RuntimeException: java.lang.RuntimeException: Duplicate class com.amazon.device.iap.PurchasingListener found in modules AmazonAppStore-runtime.jar (:AmazonAppStore:) and in-app-purchasing-2.0.76.jar (in-app-purchasing-2.0.76.jar)

So I'd like to remove AmazonAppStore-runtime.jar that comes with Unity's IAP plugin from the build, but I can't figure out how to do it.
I guess I need to use custom gradle templates, but I cannot figure out the proper syntax.

I'm using the External Dependency manager if that makes a difference.

I tried things like

Code (Boo):

1. configurations.all {
2.     exclude group:"com.amazon.device.iap", module: "AmazonAppStore-runtime"
3.     }

But it doesn't exclude it.

Any help will be appreciated, thanks!