I am not sure this is really teachable. At least the metaphor part. It is a personality trait. Visual thinking is an independent trait, and a more teachable one, but only the kinds that are based on either perception (right-brained drawing) and platonic categories (left-brained drawing). Metaphor in visual thinking requires the additional element of imagination which is not really teachable. That's why so many skilled artists can mimic others' styles, but not originate new visual thinking.

Metaphoric thinking (both conceptual in the sense of Lakoff and Johnson, and regular figurative) is not necessarily visual. In fact, in my experience, it is very rarely visual. Visual means communicate metaphoric concepts well in some cases, that's all.

One reason metaphoric thinking is not easily teachable is that it draws on a huge store of associations among relatively raw ideas and thoughts. Adults don't store raw "raw material" as well or in as much quantity, which means kids with the inclination towards metaphor need to be given the chance to store 10-15 years worth of raw material relatively young, starting as soon as they can read relatively complex stories without help (about 8-9 years) and create associations through writing and drawing. If you miss the launch window, its basically game over. I don't think adults can learn to be good at metaphor.

I am trying to create teachable material on advanced/sophisticated metaphoric thinking for adults as it happens, and the main challenge is actually selecting for those with the right personality traits who made the 8-9 launch window. If they didn't get the basics by age 21, not much can be done.