Out of curiosity, since the latest Gentoo liveDVD (12.1) has ZFSonLinux support, could that be included in Sabayon as well?
The required packages are in Portage (sys-kernel/spl and sys-fs/zfs) but not in Entropy (yet).
To be an installation option, the modules would need to be pre-compiled and loaded prior to installation.
More information here.

