You can add URL redirects so the browser thinks that it is accessing only one server:
www.server.com/ ->www.server.com/index.html
www.server.com/marketing ->www.dominoserver.com/marketing.nsf/$About
www.server.com/sales ->www.iisserver.com/sales/defaul.asp
In the example above, the browser always thinks it is accessing www.server.com.