Git Fusion and Mercurial
I've got some great news for all you Mercurial users out there: Git Fusion is for you too! The existing Hg-Git connector lets Mercurial use an upstream Git repository, and in my limited testing it seems to work fine when you point it at Git Fusion.
Now, let me repeat: This is not a solution supported or provided by Perforce. It's an open source plugin in the Mercurial community. But so far it seems to work well. If you decide to try it with Git Fusion, please let us know over at the Git Fusion forum.