I finally got the client tool working against Blogger. The problem turned out to be simple - there are a few variations on the Blogger API out there. In particular, there are two "initialization" methods listed: 'blogger.getUserBlogs' and 'blogger.getUsersBlogs'. The Blogger page lists the correct one (I misread it). So - if you grab the latest update for the 3.9 based poster, it should now work. I've tested it against a test blog I set up.
There's still a bit of weirdness - the blogger dev email list claims that you should hit this RPC entry point: https://www.blogger.com/api/RPC2. However, I get network errors (referent inaccessible) on that one. The old one: http://plant.blogger.com/api/RPC2 seems to work fine though.
Update: A couple of small caveats. Make sure you grabbed 3.55. Also, if you run multiple blogs on Blogger, the tool will only find the "first" one in an automated fashion. Here's what you can do: put the blogId for your blog in the settings, and the tool will use that instead of asking the server for it. You can then just add multiple profiles, changing the blogid for each one.