How to prevent a user from approving their own changes?

This request has come from several of our customers who want to restrict who can approve changes to a document that is undergoing a negotiation process. In particular, the desire is that it should be possible to specify a configuration such that a user cannot approve their own changes. I’ve tried to do this using the “reviewGroups” permission, which seems close, but I have not been able to figure out a way to make this work. Suggestions? Does this need to be a new feature request?

Review groups is the right option here.