It is indeed possible to create your own entropy packages. Infact you use emerge/portage to do this.
The general premise is to emerge the package you are after (via portage or overlay as you would for gentoo), and then to use equo/entropy to "detect and package" the emerged packages into entropy ones.
Assuming you are going to push this into your own repo, you should have a thorough look at the output of equo --help --verbose , particularly the community section.
The following wiki page ( http://wiki.sabayonlinux.org/index.php? ... positories
) should direct you through adding community repos (none public atm, as far as I am aware) and there are links at the bottom for creating your own( http://wiki.sabayonlinux.org/index.php? ... _something
Feel free to you shout if you have specific questions, or need more info, I think I must have made every mistake under the sun with my repo! (trying to cleanup br.4 -> br.5 debacle now!