Yes, thank you Harnold. I added some stuff in my profile "as a workaround".
My idea was to only link the Project-GC "picture" in the geocaching.com profile and put all other stuff in the project-GC profile so it would look more homogeneous.
For that it would be great if the Project-GC user can add one or two individual tabs (with individual names) that he can fill like in the geocaching.com profile with individual HTML code.