Rewrite DNS response

My LTMs are NAT'd behind Cisco ASA firewalls. I'm trying to balance sites across two datacenters utilizing two GTMs, one in each location.

 

 

The problem is that when I create a Wide-IP it uses the internal (thusly NAT) IP address which, obviously, is an RFC1918 address and not routable.

 

 

I'd like to write an iRule to rewrite the DNS response that will translate the interal IP to the applicable public IP address.

 

 

Any ideas where to start?