The Story Management facilities on the site allow you to do that very easily.
Copy the book’s URL from Bookapy/ZBookStore.
On Storiesonline Click ‘Authors/Editors’
Click ‘Manage Stories’
Click the story’s name to view its details
On top of the details, click the ‘Edit ZBookStore Ad’ button
Paste the URL that you copied from ZBookStore into field #1
You can optionally customize the ad’s text.
Click ‘Save Changes’
Done.
Optionally: You can have up to two ads. One ad can link to your page on ZBookStore.