I don’t know how these companies actually do it, but I reckon the easiest way to set this up is if you register locally as an independent freelancer or equivale

I don’t know how these companies actually do it, but I reckon the easiest way to set this up is if you register locally as an independent freelancer or equivalent. That way you take care of all that yourself. That does, of course, leave the question of how to actually get paid anonymously, as there are plenty of accounting requirements for businesses that aren’t compatible with anonymity here either.