Using the badvpn-1.999.128 ebuild, and changing the URL to https://github.com/ambrop72/badvpn/archive/1.999.129.tar.gz (and copyright date to 2014:) appears to work.
I (the upstream) confirm this is all that should be necessary :)
Oh might be a good idea to fix github's stupid URLs. This has worked for me: SRC_URI="https://github.com/ambrop72/badvpn/archive/${MY_PV}.tar.gz -> ${MY_P}.tar.gz"
+*badvpn-1.999.129 (20 Mar 2014) + + 20 Mar 2014; Julian Ospald <hasufell@gentoo.org> +badvpn-1.999.129.ebuild, + metadata.xml: + version bump wrt #505184