[TxMt] git bundle and fmdiff

I've recently switched from subversion to git for my latex projects. I find git a lot easier to use and it was absolutely painless to switch. However, I miss the ability to use File Merge to graphically display changes. (*Very* useful if you are working with multiple authors and you want to see where text has changed.

The git bundle allows you to compare things, but I would like to use File Merge instead of the standard window comparing the changes.

Is it possible to set File Merge as default viewer for diff files as you are with subversion?

Thanks a bunch!

Max