While I did not find the yaw plugin for the more tag, I did find a work around plugin.
There are some FCKeditor plugins, one of which is called snippets. Allows for inserting small blocks of code. Similar to the templates feature but does not overwrite all the
existing code. You can add a number of snippets to choose from.
Here is the link to the plugin:
Here is my snippets XML file:
<?xml version="1.0" encoding="utf-8" ?>
<Snippet title="More Tag for WordPress" image="">
<Description>Inserts a <!--more--> tag for WordPress</Description>