routing traffic to a public Kubernetes service on AWS EC2
If someone will reach this question then I want to let you know that external load balancer support is available in latest kubernetes version.
You seem to have a pretty good understanding of the space - unfortunately I don't have any great workarounds for you.
CreateExternalLoadBalancer is indeed not ready yet - it's taking a bit of an overhaul of the services infrastructure to get it working for AWS because of how differently AWS's load balancer is from GCE's and Openstack's load balancers.
Unfortunately, there's no easy way to have the PortalIP or an external static IP routable directly to the pods backing the service, because doing so would require the routing infrastructure to update whenever any of the pods gets moved or recreated. You'd have to have the PortalIP or external IP route to the nodes inside the cluster, which is what you're already effectively doing with the PublicIPs field and ELB.
What you're doing with the load balancer right now is probably the best option - it's basically what CreateExternalLoadBalancer will do once it's available. You could instead put the external IPs of the instances into the PublicIPs field and then reach the service through one of them, but that's pretty tightly coupling external connectivity to the lifetime of the node IP you use.