Hey Joe,
There's no simple checkbox for the configuration, but the same functionality is supported by using L3 ACLs. In SmartZone, this is a part of the User Traffic Profile. From the WLAN, if you "Create" a new UTP, you can add the 3 rules into the UTP (e.g. deny 10.0.0.0/8, 172.16.0.0/16, and 192.168.0.0/16) to get the same behavior.
thanks,
Marcus