It's not clear if your subproject is using the android-library plugin, but if it is, v0.8 has added a provided scope -- see http://tools.android.com/recent/androidstudio043released.
This should work:
dependencies {
provided "my.library.dependency:${version}"
}
If you upgrade to 0.8 of the plugin, you'll need to run Gradle 1.10 (update gradle-wrapper.properties if you're using the wrapper), and if you're using Android Studio, upgrade to 0.4.3.