What do you mean by a replacement in the plugin? I was hoping I wouldn't have to edit any templates. Blergh.
Fortunately I happened to know of a plugin that adds to that menu. The code (using hook showthread_start) looks something like this:
if(can_moderate($threadinfo['forumid']))
{
$vbulletin->templatecache['SHOWTHREAD'] = str_replace(
'$vbphrase[remove_redirects]</label></div>',
'$vbphrase[remove_redirects]</label></div>\n<div><label for=\"my_option\"><input type=\"radio\" name=\"do\" id=\"my_option\" value=\"my_option\" />My Option</label></div>',
$vbulletin->templatecache['SHOWTHREAD']
);
}
You'd want to replace all occurances of "my_option" with something else of course, and also the text "My Option" (and if you want to use a phrase for that, use something like $vbphrase[my_option])