I do not yet have this completed for redistribution ... but soon will. I was able to do this by creating hacked copies of Dave Winer's blogger.newPost methods, and creating a blogger.newAtomPost method. I did one quick test post, and then headed to bed. There are a couple of bugs that I have to work out, and then I was to see if I can hack this into the #upstream.xml file processing. I'd like to simply be able to put a line in the #upstream.xml file that indicates that I want to upstream using the Atom API.
If not, then I'll still end up creating a seperate tool that will be a fork of the xManilaBloggerBridge tool written by Steve Hooker. Fun stuff ... I'm glad that I took the time to write this ... it was a good learning experience.
P.S. For anyone who wants to use the xManilaBloggerBridge tool with Radio and Blogger, I found that there are two core changes to get this working ... I had to search for "metaWeblog." and comment out the calls to these methods, and then look right next to them and un-comment the "blogger." methods. Once I had done this, the basic Blogger API stuff started to work just fine. There is not support for 'titles' in the Blogger API though ... this is why I pursued the Atom API support.