For the record, I created a PR on our repository to create the proper copyright file, based on some properties, the setup can be find here: xwiki/xwiki-platform#839

Basically we have a copyright resource file we process with the maven-remote-resource-plugin (well it's not exactly this one in our setup, but it would work the same with maven-remote-resource-plugin) to put the right info: license type defined by the pom, years, etc.
We configure jdeb to put this copyright file at the right place given the package name.
And finally as we also need to put this copyright file along with the control file, we copy the entire deb/control directory, put the copyright in it and use this directory as controlDir for jdeb.