Change CAL expiration date

All,

   i am running WinSVR2K8 R2 Datacenter. My issue is I have a client that is taking up ALOT of CAL licenses. Im using CAL per Device format. I need to change the expiration lease length on the licenses. i think they set around 6months, and i need to change that to about a week. Any thoughts as to where to find this setting?