This is actually supported in the Android Asset Packaging Tool (AAPT).
I always put my psd-like files in the resource directories like this:
/res/drawable/_pre_production/ic_launcher.psd
Any _pre_production
directory will not be added to the APK.
With this approach they're in a sub-directory of the actual images' directory, but I don't see the problem with that. It is still neatly organized. ;)
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