You can also try installing Regex replace your writeups: a free nodelet hack to your free nodelet. Just edit the default regex so it works with whatever idea you have about the wiki syntax.

This has two drawbacks. Firstly, you have to remember to hit the button before you submit, though you could fix that with some addittional javascript code. Secondly, your wiki syntax to html converter has to be idempotent so if you do edits on an already htmlified preview it doesn't try to change the parts of the node that are already in html like the p tags.