It is possible, though I haven't the willpower to break down every element of the process into the finest detail. I anticipate that if you're that desperate for free gaming with your friends whilst avoiding paying Sony; you'll do your research. There is some semi-advanced networking used. I only explain the methodology here, not the specific implementation.
Each person needs:
- A Raspberry Pi (with two network interfaces, so Wired/Wireless, or Wired/USB-Ethernet).
- Playstation with games that allow LAN-gaming. Borderlands 2 was my reason for doing this.
You'll also need:
- An account at https://my.zerotier.com
Step 1) Install ZeroTier on both Raspberry PI's, the two Linux commands here work just fine - https://www.zerotier.com/product-one.shtml
Step 2) Create a network on the ZeroTier console at https://my.zerotier.com and choose an IPv4 range for the network to operate on (e.g. 172.22..).
Step 3) Join the Raspberry Pi's to the network. If you have the network set to private mode, don't forget you'll need to authorise the Pi's in the Web Control Panel.
Step 4) Connect the PlayStations to the Raspberry Pi's - wireless or USB-eth (though USB-eth is much easier).
Step 5) Utilising console commands on the Pi's, create a network bridge between the USB ethernet or wireless interface and the ZeroTier Virtual Network Interface. An excellent guide for that is here https://wiki.archlinux.org/index.php/Network_bridge using Iproute2.
Step 6) On each PlayStation, manually go to the Network Settings and configure an address belonging to your Zerotier Network.
Step 7) Go into your game and do 'LAN discovery' or similar to find your friend on the 'LAN'.
Why does this work?
Since the addresses are not Internet-routable, the PlayStation's believe you are sat on the same local LAN at the same home, not an arbitrary distance over the Internet.