No one with answer here......
The developers very, very rarely bother with these threads… unfortunately, unless someone here has already solved your issue and is hanging around to share (or you feel like shelling out the money for Varien support, which seems to be the point of this software), you’re probably out of luck.
A quick and dirty suggestion would be to find the validate() function here…
...and add a conditional to see if the user is logged in; if not, add an error. You could try checking for this:
I’m not sure what it returns when a user isn’t logged in, but presumably it’s something that evaluates to false. You could also create that test in an observer and try to attach it to the before_save event on a review, though I don’t see an _eventPrefix in that class, so I’m not sure whether it actually fires.
Hope this helps!