Set different minSdkVersion for testAndroid than for main app

Is it possible to set a different minSdkVersion for tests than for the app itself? I ask because I want to use the new Test Support Library and UI Automator for testing. However, this is only available on API 18+. At the same time, I still want to support older versions of Android, albeit not as thoroughly tested. What do I need to add to my build.gradle file in order to do this?