It strikes me that a better solution is to fix whatever tools we're using to determine what still needs to be reviewed. If someone is checking all revisions marked as "new" and needs to mark things they won't review as "deferred" to get them off the list, maybe they should instead be checking all revisions marked as "new" from particular paths. Then explicit deferral will not be necessary, and projects like SMW can go ahead and use Code Review at their own pace without annoying anyone else.