I`ve patched the kdebase-3.1.2.ebuild with the dropshadow patches from KDE-Look.org ( http://www.kde-look.org/content/show.php?content=5638 ). Just apply the kdebase-dropshadows-3.1.2.patch and put the file kwin-shadow-3.1.2.patch into ${FILESDIR}/3.1.2/ Greetings Elias P.
Created attachment 13175 [details, diff] kwin-shadow-3.1.2.patch
Created attachment 13176 [details, diff] kdebase-dropshadows-3.1.2.patch
Take a look at bug #17468, the issues are similar. Maybe in the future we will support it, but not now.
Dead old bug left to close...