Pull requests based reviwable staging instance?

Hi developers who use pull requests based work flow, have you ever worked with a flow where all opened pull requests' branches merged with shadow master behind the scene as a reviewable branch deployed to a staging server?

That is all opened PRs are still opened, the master branch stays as it is, just the mixed of PRs'branches + shadow-master gets deployed and let project manager review.

Any PR can be marked with label to be excluded and re-mark to be included, and every push to any pull request will trigger the automated build (merging all pull requests)