I am using hg-subversion, and I have 2 different hg repositories one from our svn trunk, and one from a branch of the trunk. I would like to link them somehow. At some point in the history both Hg repositories will be identical is there some way to join them? 

In other words is there a way to relate the repositories from within Hg?

The technique I am currently using is to just export the second repository over top of the working copy of the revision they share, and then commit that working copy as a branch in Hg, but I lose the history this way.

Any advice would be great