It wasn’t perfect, but was good enough to do the job.
I wasn’t able to find any good alternatives out there, so quickly rolled my own. It takes the id of a G+ user, and spits out an “atom.xml” file into the directory you choose, which you can then send to anything that can consume Atom.
The code is up on GitHub if anyone’s interested. My code isn’t perfect either, but will do the job until something better comes along: FeedPlus.
Update, Dec 13th 2011: I’ve updated the app to use the offical G+ API now, rather than relying on the json data that Russell’s app relied on. Hopefully this will make it a little more stable. Next stop, add an option to have it post to Twitter directly, rather than just writing atom.