Hi Guenter, thanks for reaching out here. Sorry for the slow response, I was out of the office all last week. MAC auth cuts down on a lot of the authentication features that we can use in XIQ, you are correct that the set up you've described is more of an "and" rather than an "or" workflow.
However, would PPSK work for your regular users? You could set up a PPSK SSID with multiple user groups, one user group with your typical known users and their standard passwords, and one user group for your temporary users, all under one SSID. Would that work for your network?