Since you do have to add someone to each stage of the workflow template, we've created workflows with fake users on each step. Then our project managers add the real users when they set up the proof.
This puts "someone" on each step, but doesn't result in a real someone who isn't actually part of that project getting an email notification about a proof. We use noreply1@proofHQ.com, noreply2@proofHQ.com, etc., but any email that doesn't really go to anyone would be fine.