Would it be possible to have a feature that allows reviewers to 'unreview' a post? That is, regardless of action taken, push a reviewed post to another user's review queue (or separate queue altogether)?
If you've done all you think you can on a post, then you've reviewed it. Even if that means doing nothing on it since you've at least read it.
If you want other people to take a look at it, whether because you're unsure of what you've done or if the post could do with more help, you can always post that into the chat room or on meta.