The answer is no, you shouldn't mix anything with a physical sunscreen.
While the thicker, mineral nature of physical sunscreens seems to invite mixing in a few drops of makeup, moisturizer, foundation, or other products to give it a smoother, silkier finish, the oils and emulsifiers in those products actually disrupt the mineral layer of your sunscreen, making it less effective.
Despite how it may feel under your fingers, mixing in other products prevents the minerals in sunscreen from forming a smooth, even layer that actually protects you from the sun.