Stepback covers are the "inner" covers often found on romance novels, teen horror, and I'm sure among other genres. There's an outer cover with a flower or something on it, you open it up, and there's a clinch picture on the inside cover (or a girl terrified by a ghost, etc.)
I have a number of ebooks whose dead tree paperback versions included stepback covers. The ebooks don't, but the images are often available online. So I could add them myself.
I don't see an easy way to manage the stepback images in calibre. There isn't either a second cover option or a two-page cover. When I searched for stepback in the forums I didn't find anything useful. Any suggestions on a simple way to get the stepback covers in place. I'm looking at well over 100 books so the less steps the better.
PS I'm also including the spelling step-back to help future searches. I have seen it spelled both ways out in the wild. And keyhole cover.