While I don't imagine what you need right now is narrow suggestions moving forward, your post does holler "bioinformatics" at me.... might be interesting to take a peek.
More generally, he might benefit from wandering through descriptions of some major multidisciplinary areas - at lot of the major action in science is happening where traditional disciplines intersect. Computational biology is huge in neuroscience, genomics and pretty much everywhere. There's also incredibly cool combinations such as connecting physics and molecular biology to build a "lab on a chip" (OK, I'm dating myself with that example), biological batteries, mathematical epidemiology, biophysics, biomechanics, biomedical engineering - the possibilities are huge. I took a quick flip through all the things they now offer at my alma mater and found things called Geography and Aviation, and Global Business and Digital Arts; I can't tell you what they are, but they certainly get the brain heading in new directions!
One thing I did many (many) years ago, when course calendars were still paper books and I was disillusioned with my major, was to simply browse the university course listings in their entirety, and mark any course that appealed to me. The resulting patterns were hugely useful and rather illuminating. Perhaps it might help to take a wander through the program listings and courses of a few major STEM universities to see what most often catches his eye?
