Here is an ebuild and a patch for this nice game. Enjoy.
Created attachment 83743 [details] zatacka-0.1.5.ebuild
Created attachment 83744 [details] zatacka-0.1.5-dirs.patch
Comments: src_compile() is unnecessary source needs to be patched so the binary is installed in GAMES_BINDIR before being added to portage. the pkg_post* functions should go away after the source is fixed up. FILESDIR and GAMES_DATADIR should be quoted sort KEYWORDS
I have no idea of where to patch sources in order to do what you say. I patched the makefile but it wasn't enough...
Created attachment 116848 [details] zatacka-0.1.7.ebuild Updating the ebuild. Did not put in portage as it is very unstable
Created attachment 116850 [details, diff] files/zatacka-0.1.7-gentoo.patch
Waiting for some new version before getting to it again