OK, so as so often happens, after asking a long, drawn-out question, I've gone off and found a working solution. Whereas when I originally tried it the "?rel-author" tag didn't work for me before, now it does. I'm ready and willing to accept that I'd done it wrong the first time around... but just in case anyone will find this ramble of any use whatsoever, here's what I did (as per Google's instructions):
- Add a G+ profile link to each article posted - such as [View Google+ Profile]([your Google+ profile address]?rel=author)
- Make sure that under the "Contributor to" section the root domain of the site is listed. You don't need to put in a link to the specific article - just the root domain.
- Test the link using the structured testing tool again - it should give a pretty much instant result, hopefully in the positive.
- Wish that you'd done this properly in the first place.