With SVN, I had a single big repository I kept on a server, and checked-out on a few machines. This was a pretty good backup system, and allowed me easily work on any of the
There is another method for having nested git repos, but it doesn't solve the problem you're after. Still, for others who are looking for the solution I was:
In the top level git repo just hide the folder in .gitignore containing the nested git repo. This makes it easy to have two separate (but nested!) git repos.