DNS failover for active sync users at DR site

Hello, We have a DR site which has our servers replicated to it. With a few
ip changes we can boot up exchange and other machines which gives users
access to resources. However my question is for our active sync and iphone
users. Our active sync users point to exchangefrontend.domain.com to get
there active sync access. That domain name resolves to our FE at the primary
site and DNS is controlled by our ISP.

How can we set it up so that our activesync users can resolve to that same
dns name in a DR event since exchangefrontend.domain.com will have a new IP

As of now we have to notify our ISP to change the IP adress of that A record
which can take up to 16 hours for us. Is there a way to do some type of
failover for exchangefrontend.domain.com to automatically resolve to the
different external IP which is on the DR side?

This was one recommendation but im not sure if my isp supports this.

"have them delegate a subzone to your Global loadbalancer (lb.domain.com)
then CNAME anything you need to wide IP (exchange.domain.com CNAME =
exchange.lb.domain.com"

Thanks