I've read that it's not impossible. You can't make something work with 100% accuracy, but that is not needed for this purpose. If you're going to reply there are no genetic racial differences, then consider sickle cell anemia and differences in alcohol metabolism.
I've also read a lot of stuff on the Internet, that doesn't make it all true. Source?
There are genetic racial differences, but the lines are so fuzzy and inconsistent that this couldn't work.