If it is a vb add-on which is using the construct_edit_toolbar function(and i think it is one), you'll have to search for the call of construct_edit_toolbar in the file and add the text you want to have into, as first parameter!
PHP Code:
// #############################################################################
/**
* Prepares the templates for a message editor
*
* @param string The text to be initially loaded into the editor
* @param boolean Is the initial text HTML (rather than plain text or bbcode)?
* @param mixed Forum ID of the forum into which we are posting. Special rules apply for values of 'privatemessage', 'usernote', 'calendar', 'announcement' and 'nonforum'
* @param boolean Allow smilies?
* @param boolean Parse smilies in the text of the message?
* @param boolean Allow attachments?
* @param string Editor type - either 'fe' for full editor or 'qr' for quick reply
* @param string Force the editor to use the specified value as its editorid, rather than making one up
*
* @return string Editor ID
*/
function construct_edit_toolbar($text = '', $ishtml = false, $forumid = 0, $allowsmilie = true, $parsesmilie = true, $can_attach = false, $editor_type = 'fe', $force_editorid = '')