Hazel, that was fantastic! I'm still laughing so much that I almost can't type!
Now for an attempt at keeping this even remotely on topic. I haven't written any L&C fic (though I did make an attempt the other day...) but I have written a couple of pieces for Farscape. However I find it very difficult to write a plot driven fic, so anything I write tends to be introspection/POV for (one of) the main characters, and even then, its usually an episode addition. So I don't usually have to worry about Mary Sue.
At the moment I wouldn't consider writting about the supporting cast as I struggle to flesh out characters without a lot of help from the show, thus leaving only the main characters. The same goes for OC's too. Especially them, since I'm aware of Mary Sue!
Loriel