Disabling USB storage on a desktop for real

Ok.  I've been around and around on all the disable USB suggestions and quite frankly I say bollocks.  I've built the ADM and tried through GPO.  I've written the script to diable via Registry.  I've disabled access to the USBSTOR drivers.  All but the ADM produced results, only not thorough enough for my needs.  I have a need often in my environment to lock these devices down solid due to virus threats and other incidents.  My network is exposed to threats unlike most.  I have users from dozens of countries using thumbdrives to share information and sometimes they bring viruses that haven't been seen yet.  It's times like these that I need to lock drives down hard and completely.  Yes I have Anti-virus and I use Symantec.  No I can't change to something good like NOD32 because of regulations.

I would prefer to allow my superiors to be able to request exception to it much like a GPO would provide.  I've been through several virus outbreaks and although we have hindered their propogation through our system we have not quelled it.  I need a solid "this works all the time no matter what" solution and I can't find one worth while.

Please give me any guidance you may have on the subject.  I'm in the middle of one of these outbreaks and am floundering as I search for a definitive way to quell the beast.  Thank you.