Expand Physical RDM beyond 2TB

I have a 2TB physical RDM drive on a server that is nearly full so I need to expand it.  I am running vSphere 5.0.0 Build1024429.  From my research i should be able to attach luns larger than 2TB with this version.  If I try to add space to the current lun I receive an error that it is not allowed, the maximum is 2TB.  If I try to create and attach and new lun over 2TB I create the same maximum error.  Is there some other configuration that needs to be done before I can create or expand over 2TB?

Thank you for your help,

Natalie