How to run multiple instance of freeRADIUS on one server

Hello, I am using freeRADIUS 2.0 on Ubuntu Server 12.04 LTS I want to know how to run  multiple instances of freeRADIUS on one server. In this case I want instance-A to have the authentication port to be 1812 and instance-B to have authentication port to be 1814. The acct port for instance-A to be 1813 and the acct port for instance-B to be 1815. I am thinking this is possible but I've been google for months now and have come up with nothing.  Can you please point me in the right direction? Kind Regards, Kwesi