Migrating svn to git with heavy use of externals

I'm a developer on the Sakai project. I think Sakai could benefit greatly from use of git because we have a huge need to track local changes while contributing back to a central codebase. I've started looking at git-svn and have managed to get a copy of our repository into git, and looked at the stuff to do with submodules as a replacement for externals. The problem is we rely very heavily on externals, for instance when we make a tag for release we tag all the modules at the same time and use an externals file to build the release from those tags. I realize that's probably not a best practice, but it's what we do. Our latest release is here: https://source.sakaiproject.org/svn/sakai/tags/sakai_2-5-0/ if you want to get an idea of the scope of the problem. How would you convert this to a git repository? I'm currently looking at http://blog.alieniloquent.com/2008/03/08/git-svn-with-svnexternals/ but that doesn't look like it would leave all the old release tags intact.