The problem that I am having has to do with the need to keep some urls of a website protected by HTTPS and the rest kicked to HTTP.
Normally, you have $_SERVER
If the load balancer is the other end of the SSL connection, you cannot get any more info than the load balancer explicitly provides. I would go for adding a http header, it may already be doing that, dump all the HTTP headers and look.
As another solution, you can do the redirection on the load balancer based on URL.