Review request as well as pull requests

In our team it sometimes happens that someone wants his/her code reviewed halfway through to vent issues and concerns about the current code.
Right now the only way is to open a temporary pull-request which is, after review, automatically declined by the reviewer since the branch isn't complete and ready for merge but this is, as I write, a temporary solution.

What we would want is a Code Review Request to accompany the Pull Request so that our developers can open a request for a review where we can comment and add tasks halfway through the development process. This would look more or less exactly like the Pull Request except there would be no way to accidentally merge the branch.