There is only 1 '
Official' cover in any book.
All the rest are just a page with an image.
So... Collect the images of the covers from your Fav site(s)
Insert a blank page where you want , Use the Editor (on that page): Click the Insert Image icon (on the page toolbar). Add CSS styling to taste.
Repeat for each image
Alternately, you could walk the (canceled) covers to their new home
Add a cover (tools:add cover), then remove the 'cover' semantics for both the XHTML and image /It looks like you need to edit the OPF/
The advantage is Add Cover does all the SVG code
