How about adding a little filter that scans for the use of braces or nested parentheses in peoples post and very explicitly complains if matching posts does not contain the required formatting tags.
A huge majority of new posters are clearly completely unable to read a few lines of posting instructions and don't seem to look at the preview and notice something strange about their code.
Since garbled source code is so hard to read, it wastes a lot of time for all people on this board and it is hard not to be rude after reading the 10th thread with unformatted code.