So in teaching creative writing, I went over this with my class. The standard types of stories, and how there really are no new ideas, just new executions (call the headsman!). I firmly believe that. The trick, I think is that the execution must be a fairly radical one. Subtle executions don't gain enough notice.
So it's time to get crazy. Look at those weird combinations, and see if there isn't something that can make them work. Not unlike water (I wish this was a Bruce Lee metaphor, but alas). Two volatile chemicals combine to make a molecule that extinguishes such conflagrations, and is the building block of life itself.
Maybe such seemingly crazy combinations will make something entirely natural, but in a way that no one ever expected the disparate themes to combine.