It’s not possible! Dang!
Their system, for some odd reason doesn’t expose a users public stream as an RSS/Atom or other consumable content.
It’s odd, so many other services provide this.
With Google Plus however you cannot, they simply don’t offer it.
There was an offering on http://plusfeed.appspot.com/ but that service is now offline.
And are many other’s talking about this exact same issue.
There is also a service provided by Yahoo that converts pages to XML or other feed types.
But lately it’s been throwing some 500 level errors.
We’ve come up with a solution however, you can use the services at Blstr! Plus Feed to make this work.