I have a page at host1.mydomain.com/page_from_host1.jsp and an HTML page at host2.mydomain.com/page_from_host2.html. host1 is an IIS7/Tomcat box and host2 is an IIS7 box.
By using following C# code "Enable Proxy" can be checked/enabled
ServerManager servMgr = new ServerManager();
Configuration config = servMgr.GetApplicationHostConfiguration();
ConfigurationSection proxySection = config.GetSection("system.webServer/proxy");
proxySection["enabled"] = true;
servMgr.CommitChanges();