Here is my custom policy implementation. It allows to run child policy if user does not have certain permissions (is not member of certain group).
It can be used with custom path policy from TFS power pack and ColinsALMCornerCheckinPolicies Then it will be possible to ask for code review only for certain projects|files|folders and only if user has no permission to check-in without code review.
https://github.com/oleksabor/GroupMembershipPolicy
You have said that had migrated from TFS but I'd like to leave answer here because have not found solution for original question.