The UIShell navigation technique used in JHeadstart is similar to what is described in this blogpost: https://blogs.oracle.com/jheadstart/entry/core_adf11_uishell_with_menu
The easiest way to include a custom jjsff page is to create an additional group in JHeadstart, set the layout style to form, add one dummy unbound item, generate it once, and then switch off page generation for this group. You can then copy and paste the content of your custom page fragment into the page fragment you generated once.
I checked the blogpost, the UIShell navigation technique used in JHeadstart is brilliant and the blogpost is exactly to the point! Thank you very much.
Yes, you are right one could add a manual page by the help of JHs at the first place but I was eager to learn how does the navigation technique work.