Hallo Fitzcarraldo, hallo Stupot.
Before I was busy for 2 days, I made a new try to realize your suggestion to rebuild kdeplasma-addons with USE="desktopglobe"
For that I've read more emerge help sites. Then I combined your commands with those from in the websites.
That's my solution now (done in konsole):
1. emerge --sync
2. (Re)install gcc compiler 4.3
3. USE="desktopglobe" emerge -1v =kde-base/kdeplasma-addons-4.9.0
4. Complete Reboot of computer.
These 4 steps were my stairway to heaven. I've added my Marble chosable as Wallpaper now.
Thank you a lot,
-Linuxfluester, Core i5, 6 GB Ram, NVidia GT320M, Sabayon X
p.s. As all I see on package site https://packages.sabayon.org/show/kdepl ... 5,standard
the USE flag is still set to "-desktopglobe"