192.168.0.6 = IP on my Orange network
10.0.0.119  = Remote host on other side of the VPN
172.16.0.6  = IP that the other end wants me to be

iptables -t nat -A POSTROUTING -s 192.168.0.6 -d 10.0.0.119 -j SNAT --to-source 172.16.0.6
iptables -t nat -A PREROUTING -d 172.16.0.6 -s 10.0.0.119 -j DNAT --to-destination 192.168.0.6