Do any refactorings in separate reviews, and say things like "REFACTOR_ONLY:", with a rule that none of the code changes behavior.

That makes reviews a lot easier. The review starts from "nothing should be changing" and then reviewers can pattern match on that.

Otherwise, the reviewer is re-evaluating every line of code to make sure nothing has changed. That's really hard to do properly.

The version control systems I've worked with have allowed queues of changes, each one reviewed independently. As I'm developing, if I need a refactor, I go up a commit, refactor, send out for review, rebase my in progress work and continue.

I send out a continual stream of "CLEANUP:" "REFACTOR_ONLY:", and similar changes with the final change being a lot smaller than a big monster of a change.

Your reviewers will appreciate the effort.

Plays the metric game (if you're working in that type of org) without being evil too.

These are problems with a code review tool. Not a code change problem.

https://github.com/ReviewStage/stage-cli looks like an interesting start on that subject.