Envisioning what you said and my interpretation, if it's all along the same lines I'm not feeling that there would be much of a "pattern" to see. My son is very monochromatic with his tastes too.
Is he open to incorporating other lighter shades of whats been picked out?
If not, I'd make a scrappy like 9 patch, maybe making the squares somewhat bigger to show the difference in the prints a bit better, so it doesn't look all blended as much. ?????