SIP codes and Dial Status

Our carrier has the ability to block calls to numbers on the National DNC list. Every call that we send to the switch is checked against the DNC, and if a match is found the carrier returns a 503 (DNC Blocked).
Now, all of these 503s are set as an NA by Vicidial. So, naturally these numbers are dialed over and over, but blocked each time.
Is there a way to tell Vici that the "SIP Hangup Reason" (DNC Blocked) needs to be added as a DNC and not a NA?
Now, all of these 503s are set as an NA by Vicidial. So, naturally these numbers are dialed over and over, but blocked each time.
Is there a way to tell Vici that the "SIP Hangup Reason" (DNC Blocked) needs to be added as a DNC and not a NA?