ShrinkWrap Resolver do not currently have an API binding for Gradle. However, I'm pretty sure Gradle can use Maven repositories. Maybe you can create a test-pom.xml file and somehow import it in your gradle build while using test-pom.xml via ShrinkWrap Maven Resolver in the tests.
Would that work for you? Do the effort seem reasonable? The untimate way is to create ShrinkWrap Gradle Resolver, but so far nobody is working on this.