Glyn,
Isn't the Add 9 essentially the same thing? If you want the traditional Sus2 chord just remove the 3rd under the details section of EzKeys. i.e. in the Toontracks EZKey Wheel, C Add9 would be CEGD, C Add9 without the 3rd would be CECD (Csus2) unless I am missing something from your question. Hope this helps.
Regards