Keys/Codes for upgrading to a new group plugin

Does anyone know any plugin that allows you to generate keys/codes in the admin cp, and then allow people to use these keys/codes on the forum to upgrade to new group?

I have only found this plugin here:http://www.mybbextras.net/Thread-Ultimate-Subscriber-Gift-Certificates but the thing is it's literally impossible to register to that forum as the captcha isn't working.