|Ever hear of the OSI model? It is seven layers and is the blueprint for computing design.|
Networking is layer3 - ip routing
Applications are layer7 - IE
Unless the app has a ip console to specify a route or server you have NO control since this is handled at layer3.
I have given you two choices. Manually enable/disable the state interface when you want to get on the internet or try setting the metric on the state line higher so it is the less preferred route.
Your choice. There is not a third option that I am aware of.
Well there is but its not practical. You get a dual wan port router, have both state and internet go into it, configure the rules and then only connect one pc nic to it. How you configure dns, or in this case which dns server you use gets a bit more complicated.