Replying to myself again...
I could do a quick hack to allow blocked users to edit their own talk page, if that's what you want. It's a much simpler feature to the other thing I'm working on at the moment, i.e. per-article blocking.
This is done, enabled on en only. It can be enabled on other wikis on request.
Anyone willing to defend this should go to http://tinyurl.com/8bxwp , because it's heading for a quick demise.
-- Tim Starling