Nginx AWS ELB & AKAMAI Integration

I'm currently facing a problem with one of my infrastructures; I have some nginx web caches reachable to port 7321 with an internet-facing ELB at the top listening on port 80. Akamai use the ELB as origin to retreive stuff.

I would like to prevent users\b0t to directly connect to the ELB origin and force a 301 to the Akamai\Website DNS.

With CF (Cloud Front) is pretty easy to accomplish, they publish a json list that contains all the IP/sub of the CF cache edge locations http://ift.tt/14ZcFtP so I use it for create the "policy"

Some of you guys had the same problem?

Thanks a lot.