I've created portletapi ebuild. Though it's named portletapi, its name and version should be discussed yet.
Created attachment 97425 [details] portletapi-1.0.ebuild
Created attachment 97426 [details] portletapi-1.0-build.xml
The most up-to-date ebuild can be found here: http://overlays.gentoo.org/svn/proj/java/migrated-java-experimental-overlay/dev-java/portletapi/
Added to portage. Thanks for contributing!