Having decided to move my blog to Jekyll, I went looking for solutions. AzizLight's class proved the simplest, but fell short of what I wanted.
This version has been modified to be runnable as a command-line script (help available via -h) and, aside from category permalink continuity (which I'm working on), produces a ready-to-use _posts directory for your Jekyll blog.
Full details on the changes are available in the git commit log.