1. run apache or port 81 or whatever port you'd like, just not 80
2. define a web server external app, address should be "127.0.0.1:81". no need to set "environment".
3. add a script handler for suffix "shtml", using the web server external app as handler. If can be done at server level or vhost level.
If any question, please read the online help first for each individual configuration option.