Are you able to assign peer reviews to items NOT uploaded as an assignment? For example, if evaluating a poster presentation, can you have students peer review it? If so, would the peer review be an "assignment" rather that an actual "peer review" attached to an uploaded assignment? And if it is its own assignment, how does the feedback get back to the presenter?
Is the solution to have something uploaded as the assignment (even just a blank page) so that students can access the associated rubric and peer review the poster presentation?