In discussion with QlikTech we've been informed that this is not possible. The standard way of doing this at the moment, according to our technical contact at QlikTech, is by reloading using a batch-script and running that script as the appropriate user. In our case that also requires the user to have a valid QV-developer license. I'm unsure if that's always the case.
I really wish this kind of functionality was be built into the Server/Publisher and I'm sure I'm not the only one since QlikView is frequently used in information sensitive industries like Finance for example.