How can I create a FreeBSD package using EPM that has the ORIGIN @comment?

Question

I'm building packages of our internal software products using EPM, and over time these packages (of which we have a large number) clutter up the output of pkg_delete and pkg_add with the following general kind of messages:

err: pkg_add: package MYPACKAGE has no origin recorded

I can see from some old FreeBSD lists that the +CONTENTS file in the package must have a line like this:

@comment ORIGIN:some_source_path

What I don't see is a way to get this line in place using EPM. Can somebody tell me how to do this?