You can setup a tunnel over SSH with -w option as below.
Try it at home, not server!

Server side
===========
ip tuntap add mode tun dev tun0
ip addr add 192.168.16.1/30 dev tun0
ip link set tun0 up
iptables -I FORWARD -o tun0 -i <public-interface> -j ACCEPT
iptables -I FORWARD -i tun0 -o <public-interface> -j ACCEPT
iptables -t nat -I POSTROUTING -o <public-interface> -j MASQUERADE


Client Side
===========
ip tuntap add mode tun dev tun0
ip addr add 192.168.16.2/30 dev tun0
ip link set tun0 up
ssh -NTf -w 0:0 <username>@<server-ip>
ip route add <server-ip>/32 via <default-gw>
ip route add default via 192.168.16.1 metric 10