What I'd like to do is to write a post in WLW and have it publish to both my personal blog *and* to my Posterous blog. In other words, at the end of the OnPrePublish method, return true instead of false.
Obviously there is more to this than meets the eye: the current behavior has to be maintained, which indicates that there should be another option. This extra option means that there should be a checkbox in the Options form to set it: "Publish to underlying
blog as well?", default unchecked.
The problem about doing the round-robin route (WLW -> Posterous (using my blog as the underlying setup) -> my blog) is that Posterous doesn't return the category and tags to my blog's MetaWeblog entry point.
At the moment, I can create a post in WLW, publish it to my normal blog, then switch the blog option to Posterous and publish it again, but that's a bit error prone.