I'm in the same situation. Got a hobby writing app slapped together that has a built in Markdown converter. I want normal people to use it but the idea is to focus on the writing, not the formatting so there's no buttons for WYSIWYG editing. I think I'm the right context Markdown only would work. In my situation I'm probably just going to throw up a short intro to Markdown tutorial for people who want to format their writing. It's okay in my case because the focus should be on words, not formatting and I have a hunch regular folks can learn Markdown within 20 minutes at most for the most part.

Shameless plugs: http://writeapp.me (source on github at http://github.com/billpatrianakos/Write.app)

shameless plug too, feel free to try my DOM > markdown project. should be easy to get any editor that generates DOM to emit markdown

https://github.com/leeoniya/reMarked.js

demo: http://leeoniya.github.com/reMarked.js/