ip neigh add proxy "IP" dev "interface"

• Disable masquerading

  iptables -t nat -I POSTROUTING -s "IP" -j RETURN
  

• Add on startup

  crontab -e
  @reboot /sbin/ip neigh add proxy "IP" dev "interface"
  @reboot /usr/sbin/iptables -t nat -I POSTROUTING -s "IP" -j RETURN