Do you mean the "Download Social Metadata (tags/rating/etc.) for the selected book" option? I just found that, but am only able to access it, it seems, when editing books individually. I could be blind - I'm tired tonight.
But I've gone ahead with the stock "download metadata" and I'll tidy up the stuff I don't need after. It's not a big deal. And once it's done, keeping up with the one-two books added won't be a big deal.