The main purpose is for website optimization and organization. I want to pull all of my img, css, js,... files from from this subdomain the I don't get blocking from trying to download everything from the same domain. I had tried the method you suggested and still might stick with that, but it doesn't handle any dynamic files (php). If I visit a .php file the browser automatically downloads it. So just to clarify, your suggested method is the only hacky ("but it will be overwritten by Plesk") way to to point a subdomain to folder in the primary domain?
Thanks for the help.