Not sure if this helps entirely, but....
The homepage of git-tfs points to: http://sparethought.wordpress.com/2011/07/18/how-to-establish-git-central-repository-for-working-against-tfs-with-git-tfs-bridge/ for an automated guide.
If you take a look in the comments, there is someone talking about a 2-way synchronisation.
UPDATE (Taken from comments)
https://github.com/git-tfs/git-tfs/blob/master/doc/commands/bootstrap.md is the specific command required.