help with porting vagrant

[Nikolai Lifanov]

Hello.

I am trying to port Vagrant (http://vagrantup.com/) and I hit somewhat
of a wall. I want to use all of the rubygem magic in bsd.ruby.mk, but
I need to build the gem first ("gem build vagrant.gemfile").
It seems that I can't override the DISTNAME or EXTRACT_SFX if I want
to use USE_RUBYGEMS, and it needs to be downloaded from GH as a .tar.gz.

How can I fetch/extract/build a rubygem and then use the logic in
bsd.ruby.mk to install it cleanly?

Thank you!