Hi godfather,
I haven't tried these before but....
If you're looking for just a 5 o'clock shadow, the Paynes Grey oil paint should work. I've heard of adding on very tiny dots and blending them into the flesh mix while wet.
Another route might be using pastels after the flesh paint is dry.
If you want real stubble, maybe try Mr. Surfacer 500 on the face before priming it. I'd think you could paint it on with a brush and stipple it while still wet.
Just a couple of wild ideas :lol:
Good luck and let me know what you do. I'm curious to hear how it turns out.
Craig