Linux – Configure VirtualBox webserver to see visitors IP address

I finally managed to move my server to VirtualBox virtual machine.

VM is running in NAT mode. I have forwarded necessary ports, including the port 80 which I first fowarded with iptables to port 8888, and then forwarded via VirtualBox to port 80 on guest OS.

-A PREROUTING -i p10p1 -p tcp -m tcp --dport 80 -j REDIRECT --to-ports 8888

Everything works great! Except… I can't see website visitor IP addresses from PHPs $_SERVER['REMOTE_ADDR']. I only see 1 IP address, which is the host's NAT address, I assume.

How do I configure my system (host OS and VirtualBox) to be able to run webserver and see visitor's IP addresses?

My host is directly connected to Internet via 1 fixed IP address. Getting another IP for guest's bridged connection is not an option (it's already a pretty expensive internet connection).