hmm - I think its possible by using javascript so that the view source would say something like:
""I spoke to <script type="javascript">document.write(base64_decode('gt Ydhjdjijrh8aeh'))</script> today and we were talking about... "
but I'm sure there's no such function built in... or am I wrong?
I know there is a product/plugin here that obfuscates email addresses on the boards. Let me link you to that, perhaps you can work on that to get what you need...