The content item documentation seems to indicate that you can return multiple links :
"After the Tool Provider receives the
ContentItemSelectionRequest message it will need to send back a
ContentItemSelection message that includes the
content-items they wish to send back."
But the grade passback documentation seems to indicate that you have to create each assignment manually then choose the LTI link that will return the grade.
What we would like to do is create a LTI content item tool to choose a configuration of an ebook which would return the chapters as LTI links that can return a grade per chapter.