A possible workaround:
If you have the ability to create a DNS entry and affect the response based on topology records (such as the querying DNS server) you could in essence create a specific response for your region the DNS server(s) are responsible for. This could also allow you to return a different response if the preferred proxy (or group of proxies) is unavailable.
Enhanced DNS devices such as F5 GTM/LTM are capable of this, I'm sure there are others.
