A simple edit to the "post new thread"
with all the "please post your code" replies, and i have made quite a few as well, would it not be an easy try to mod the post box to maybe between the "title" and the "message" to make a nice red text comment about "if you have code issues, please post your code" ?
But then the hard part would be formatting it into code tags. Say they do post code but don't use the tags, I can't think of an obvious way to tell on submit. sure the occurrence of a < would set off the php code but on css or html it would be close to impossible.
Maybe just a little line saying please post the working idea would be sufficient in a little way. Too many people ask a question and we either ignore it because there is no code or we reply to post the code they have.