Enter `su` to become root. (Double check with whoami afterwards).
Enable wifi tethering and ensure your data connection is working (connect to VPN)
Run `netcfg` and note your interface names (typically tun0 and wlan0 (ignore m.wlan0 or similar, only take the one with a real mac address), as is on my SGSII)
Double check the subnet for your wlan0 device and enter the following commands:
iptables -A POSTROUTING -s 192.168.43.0/24 -j MASQUERADE -t nat
(setup a postrouting entry for the tethered devices subnet, implementing NAT)
iptables -A FORWARD -j ACCEPT -i wlan0 -o tun0
forward packets from tethered devices across the tunnel
iptables -A FORWARD -j ACCEPT -i tun0 -o wlan0
forward packets from the tunnel to the tethered devices
Note, because you are using NAT, you will need to configure port forwards on your Android device to be able to run servers etc on tethered devices. Unlikely you'll need to worry about that though. Feedback if it worked or not. Posting this now from my home IP thanks to OpenVPN for Android and these iptable rules!