How to round-robin UDP packets w/ iptables?

My goal is to receive a UDP packet from a single port on a public interface and redirect it to multiple ports on 127.0.0.1 in a round-robin fashion. The messages are simple one-shot receive/reply messages, so I don't need a persistent mapping, but I will need to make the replies appear to have come from the port on the public interface. I believe it will be much more efficient to do this translation in iptables then to have a user space process act as a proxy.

I haven't been able to find an example of anyone doing anything similar, and its not 100% clear if this is supported, or if I would want to use the REDIRECT or BALANCE targets or some other method. Could someone get me started in the right direction?