Android: Remove a dependency from a build variation

Android's build variations (flavor and buildType) feature is an awesome way of maintaining several cuts from the same source code. I've used it both for white-label branding solutions and for Free vs. Pro versions. However, sometimes you have different dependencies between the versions where you will usually have to live with the fact, that all variations of your app gets the superset of dependencies. There are ways around this however, and I used it to shave over 400Kb off from a Free variation to a Pro variation. The problem Java is a static language, so you can't just go ahead and rely on late-bound linking and have Proguard slice and dice. It's unclear to me, whether the Android variations mechanism extends to Java source code, but I don't think it does. It's also unclear to me, whether an SPI approach could be used, letting the build class-path inject different implementations of some API for use at compile-time. What IS clear to me however, is that ...