Please check whether the use of 'einstall' in this ebuild is actually needed. From a quick glance at the Makefile, it seems to have proper support for DESTDIR. Therefore, if possible please replace the call to 'einstall' with proper 'default' or 'emake DESTDIR="${D}" install'. Thanks.
This won't work here, because mg doesn't use autoconf, and the GNUmakefile is setting prefix=/usr/local. So we need to pass proper prefix and mandir, which is what the einstall shortcut just does.
Since the install is trivial enough (it installs a single binary and its manpage), I've replaced einstall by dobin and doman. So it won't show up in your future scans.