Just had a moment to check in here! Great work, Ian, and I like the final idea best of all. As far as I'm concerned that works great and I'd be happy to implement that on the site... um, when I get time.
It's ridiculously busy at the moment.
In answer to the landscape/portrait problem, it's not really a problem at all because I dealt with that one ages ago. ALL book covers images are confined to 280 wide x 290 high. Most are portrait shaped, so are 290 high. But some are very wide.
Mary Mouse is a good example of this -- there are no reprints for this particular one but all covers follow the same rules anyway. So we just need to make sure to allow for 280px wide (plus a bit of space) as I have done in the current first edition setup.