After getting the answers I needed from the OAuth list, I decided to go back to hacking at getting OAuth to play nice with AtomPub on my host.  I am pleased to report that it now works!  It requires a two-line patch to WordPress (for my host anyway, YMMV), and I had to change the wp-oauth plugin a bit (lastest in SVN), but I have successfully posted to my test blog using a remote AtomPub script authenticated using OAuth.

See some example code.  The future is bright!