You could use some sort of cloud service: for example, Dropbox. One of the main ideas behind of Dropbox was to have a way for multiple people to easily edit stuff collaboratively. It has a very easy user interface for such things (just keep the deck in a synced folder), and you can do it even without all the technical fiddling you'd need for git.
You know the drill - If it's worth saying, but not worth its own post (even in Discussion), then it goes here.