I figured it out! The answer is to NOT specify the namespace in the style.
<?xml version="1.0" encoding="utf-8" ?>
<resources xmlns:android="http://schemas.android.com/apk/res/android">
<style name="CustomStyle">
<item name="android:layout_width">wrap_content</item>
<item name="android:layout_height">wrap_content</item>
<item name="custom_attr">value</item> <!-- tee hee -->
</style>
</resources>