Articles: in two parts: One visible and the other one clickable.. ?

You have to write two papers. At the end of the first one, put a "next" link, linking to the second paper.

The second paper will be accessible but in a way hidden (meaning it will not be displayed in the side paper box.) To that purpose, when you write the second paper, give it a title but leave the "category" case empty. In that way, the article is not listed in the paper box. You have to link it from an other paper to make it accessible.

English transation to update. Any volunteer ?