DNS-Record TTL on worst case scenarios

i didnt find a nearly good solution for this problem yet:

imagine, you're responsible for a small CDN network (static images), with two different datacenter. the balancing for the two DC is done with a anycast nameservice (a nameserver in every DC, user gets on nearest location). so, one of the scenario is that one of the datacenters goes down completly. you can do a monitoring on the nameserver and only route to the dc which is still alive, no problem. But what about the TTL from the DNS-Records? Tiny TTLs like 2 min. are often ignored by several ISP (e.g. AOL). so, the client doesn't get the IP from the other Datacenter. what could be a solution in this scenario?