GSLB design for few small number of source addresses

We are trying to design a load balancing solution that will take high volumes of traffic from a client with few IP addresses (even just 1) and evenly distribute between our datacenters. Even on a transaction by transaction basis going round robin.

Using a DNS based solution we run into the following - Clients may not respect TTL value that have been assigned and will swing traffic unevenly. Causing large spikes and not spreading the traffic evenly.

We are thinking to somehow route/proxy the traffic through another endpoint in or out of our network. Any suggestions? Thank you.