Aaaarrgghh ... the Drupal mantra - "there's a module for that" - didn't hold true! There was no module. I had to come up with a solution; a solution to a problem that should have been simple (it was in the end).
It's not often that a poem puts a shiver down my spine every time I read it, but Primo Levi's 'Song of Those Who Died in Vain' is certainly one of them.