Ok completely without wordlets (because I'm being lazy

).
In public_common.pl. Find:
[/code].
Add below:
</pre></div></div>.<br>Find:<br><div class="ubbcode-block"><div class="ubbcode-header">Code</div><div class="ubbcode-body ubbcode-pre" ><pre>
.
Add below:
[code]
.
Change the text to what-ever you wish, and insert a gif file for ubb-spoiler.gif in your non-cgi directory (for the button). You might need to move that last line up or down a few lines depending on where you want the code button to appear.