I think that a very simple code-detection could already be sufficient. If the post contains something, which remotely resembles Perl code, and it dosenīt contain a single <CODE> tag, then wrap the whole post in <CODE> tags.

This is very crude, and should be toggled off in the preferences, but if you are smart enough to realize that you have user preferences, you already have learned enough about Perlmonks to know that you can use the TT><CODE> tags for your Perl code.