Trying to work around a design caveat at work, I did some digging and found out I could pass EXTRA_PKG_ARGS to pass -X appropriately to exclude some files with pkg_install. Problem is that an equivalent isn't readily available for pkgng, and because of how the targets are constructed it's not apparent how I would be able to exclude files in the pkgng manifest.
A framework for excluding files should be provided that works with both pkg_install and pkgng.
Over to maintainer
Till now no maintainer feedback!
Well this is a feature request, there is a mechanism planned for one day.
I kept this ticket open, not to forget, you are right I should have at least ack it.