When a user wants to create a request, the form is prepended with a "email" field. Captcha is also enabled. When the user submits, the user (email) is instantly created with a random password, and reporter of the request is set to newly created user. The user is taken to the request details (and logged in), and a reset password email is sent.
The caveats are: knowledge articles cannot be shown.
Note: if your project is limited to customers who are added to the project, you need to add the UltimateTheming.AnonymousSDUser to that list.
Request Types visibility
The request types of a portal can be restricted wrt. visibility. (Sys)Admin goes to any portal, then in the Ultimate menu, Request types visibility can be clicked. A request type can be restricted to groups and/or organisations (at least one should be fulfilled to be able to view). A request type also can be disabled. If nothing is set for a request type, then it's visible.