Using whereused results in a workflow to notify users

I'm working on a workflow to obsolete files (i.e. change state to Obsolete and move them to a folder that has limited access). One of the requirements is to also notify the users of the file that is being made obsolete. I've looked through topics here and it seems that the preferred way is through QueryBuilder. Has anyone done this with expressions within a workflow? I'm not having a lot of luck finding methods in the JavaDOC that seem like they might work.