You say "The ADSL will terminate in the USA via VPN connecions". To me that sounds like the clients are connecting via adsl to a USA based vpn server. Which makes me wonder why you would want to use vpn if the clients are able to connect overseas without worrying about a cap in the first place?
Or have I misread something and it’s actually a local vpn server which gets its bandwidth via an overseas source by yet another vpn connection?
If the clients really are connecting to the USA server directly I think everyone would love to know how you are getting around the telkom cloud capping!