You can bind multiple public ip addresses to an external load balancer.
Then you create NAT rules directing http/https to custom ports on the firewall, say http-8001, and https-9001.
Then NAT rules on firewall can change custom ports back to http/https on internal server or internal load balancer.
At some point you will hit a limit as to how many public ip addresses you can bind to the external load balancer, but it is a soft limit that can be changed by Microsoft at request.
We are doing this for production and development servers and so far it appears to be working great!