The prewriting posts to your individual blogs are meant to be on the formal papers only. Don't worry about doing the pre-writing for past papers, only for those on which you are currently working or will work in the future.
Publish your formal papers either via google docs including me as a collaborator (my preference) or via the class drop box.
I like google docs because you can invite viewers or collaborators, and the immediate feedback you can get is a useful tool in writing. I also like the online web writing and production tools because many web teams are using them as basic tools for working at a distance and asynchronously.
Having said this, one of the mistakes I've made is in not paying enough attention to how UAT students are used to turning in assignments, so I'll be happy to accept assignments in the class drop box or the Q&A forums.