What about visualizing the picture of a face ? Or alternatively, like you seem to be able to visualize 3d structures, can you imagine a wax or clay sculpture of the face of the person (i.e. if you have a sculpture laying around which has a face take a look at it and try to visualize it in your head), or a coin head profile.
Once you get it to successfully visualize with one way morph it continuously into the case you don't successfully visualize yet and push the frontier. For example if you get it to work with a small sculpture try it with a bigger one.
Or try to look at a real person face as if it was a sculpture or an object. Try changing the way you gaze at the face. Sometimes, even more so with people we care about, we don't look at them like we would look at an object but we are rather trying to look at the soul behind the mask.
With faces, it's odd. When I go to visualize someone, I kind of get a fleeting glimpse, and then it fades and I can't make out anything except, somewhat blurred, their hairline. No face at all. I'm pretty sure I know exactly what they look like - the recognizer is absolutely fine - but if I try to construct an image, it goes away. On the other hand, if I had to, I could probably draw a reasonable likeness from memory by a process of successive refinement, or I could sculpt a likeness from clay. But visualize internally - no, can't do it.
I think it might be that when I'm fully awake, I can't maintain detailed visualizations very effectively. Faces are really important to us, but perhaps imperfect visualizations of faces fail to pattern match well enough against my recognizer, and so it blanks them. Like I say, I get the briefest glimpse in my visualization, but then it blanks. But maybe I'm over-rationalizing, and my brain is just weird.
Once you get it to successfully visualize with one way morph it continuously into the case you don't successfully visualize yet and push the frontier. For example if you get it to work with a small sculpture try it with a bigger one.
Or try to look at a real person face as if it was a sculpture or an object. Try changing the way you gaze at the face. Sometimes, even more so with people we care about, we don't look at them like we would look at an object but we are rather trying to look at the soul behind the mask.