It is not necessary to set ICS as a gateway. ICS could be situated next to regular network member and be in charge for some services like proxy-server, mail or web-server.
In these situations it is enough to have one network interface only.
In the above example ICS is installed the same way as normal user PC. We create a normal network with any free IP address in the existing subnet.
In the «Routes» module we create a default route via the current gateway. We use as destination External addresses ranges, select connection type - gateway and put 192.168.0.1 as a gateway. Also you should touch checkbox «Use NAT» to prevent asymmetric routing.
This way you can specify ICS as a proxy server and get Internet access.