Ah, that's an interesting way to re-direct traffic.
Realistically the only way to do this properly is to run a lightweight DNS server locally with a set of rules to re-direct traffic for some lookups to one one server and for the rest to another.
The other way to do it is this:
The unblock-us DNS server simply return their own IP addresses for the supported services, then all your traffic is routed via them. You could simply setup the IPs for the domains in your hosts file and hit their service that way - only down side is that they do this dynamically across a number of servers and you have to hit a specific server. If they change it, move it or it's down for maintainable then the service will stop for you.