Ovberlib is already used in the AddOn, all you need is to add the additional features under:
/admincp -> vbulletin-glossary -> crosslinking -> userdefined settings.
There you can change the look-like of the popup or bubble. Actually that's what i understood you wanted to do.
The only thing which is needed to get changed is to add
PHP Code:
<script type="text/javascript" src="overlib_bubble.js">
in the headinclude-template of the glossary and upload the .js-file to ftp. That#s about it.