We've used the Workflow plugin to define new states for our code review process, "Pending Review" and "Pending Merge (Approve)". The workflow is that the bug fixer assigns the case to the reviewer and sets it to "Pending Review" when they have a proposed fix, and the reviewer assigns the case back to the fixer and marks it either "Pending Merge (Approved)" if the fix is okay, or "Active" if it's not.
However, our users often forget to assign the case back to the fixer after reviewing it and marking it "Pending Merge" or "Active". In the workflow plugin for the default assignee, it doesn't look like there is a placeholder for "previous owner", which is what I'd probably put in here.
I have considered changing the "Pending Review" and "Pending Merge" states into "Resolved" statuses (instead of "Active" statuses), but that seems like it would mess with EBS. It would also be confusing to our users since they would have to click "Resolve" instead of "Edit" to mark the case "Pending Review". However, that would make the bug fixer into the "case resolver", so I'd be able to auto-assign the case back to them when it's marked Pending Merge or reactivated.