Managing EDO licenses

Hello,

We are implementing disk-to-disk backups using NBU 7.5 and HP's StoreOnce B6200's.  We have 390 EDO licenses (390TB).  Since there is no metering system within NBU that will alert you of usage, how are others managing these licenses so that you do not exceed the license allocation and be faced with a true-up bill at the end of the year? 

Thanks in advance.