How to set in-post pagination vertically instead of horizontally?

I have to split my posts into several pages with <!–nextpage–> and use <!–pagetitle:–> to add a title to every page. Works great after I found this:
https://wordpress.stackexchange.com/questions/11578/custom-page-links-for-paginated-posts-wp-link-pages-nextpage-quicktag

BUT: The in-post navigation shows of horizontally … what looks horrible if I use longer pagetitles. So I would like the in-post navigation to be seen vertically, like this:
Page 1
Page 2
Page 3

Unfortunatelly, I coulnd’t post on the site above, so I’m strating this threat here, hoping that someone has an idea how to manage. A simple
doesn’t do … ;))

Can anyone help?