Well, if you presented them with list of 100 partners each with 20 page of privacy policies and they accept it within 10 seconds it should be tricky to argue that user actually read it all.

You could, for example, require that user answers very specific questions regarding 10 randomly selected partners and how exactly they can use the data ("is partner x allowed to build very detailed profile of you and target you with political adverts that are designed to manipulate you?").