If done in good faith, four like-minded authors in the arts who agreed on a project of work could co-author four papers together and have the REF return of each sorted. If they are from different institutions, this would certainly be a more efficient way of meeting the framework's requirements. It might be viewed as a cynical exercise, but perhaps viewing it that way would be a sign that we haven't yet changed our mindset. If genuinely collaborative work became the norm, it wouldn't be viewed with suspicion.
How to game the REF